FCpSS|.S 

C.  8lt 


THERMAL  BELTS  AND 
FRUIT  GROWING  IN  NORTH  CAROLINA 

Harvey  J .  Cox 


THE  LIBRARY  OF  THE 
UNIVERSITY  OF 
NORTH  CAROLINA 


THE  COLLECTION  OF 
NORTH  CAROLINIANA 


FCP55i.5 

C87t 


W.  B.  No.  796 


U.  S.  DEPARTMENT  OF  AGRICULTURE 
WEATHER  BUREAU 


MONTHLY 


\ 


WEATHER 

SUPPLEMENT  No.  19 


REYIEW 


THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA 

By  Heney  J.  Cox,  Meteorologist 


APPENDIX: 

THERMAL  BELTS  FROM  THE  HORTICULTURAL  VIEWPOINT 

By  W.  N.  Hutt,  Former  State  Horticulturist 


r 

Submitted  for  publication  February  7,  192ff 


W.  B.  No.  796 

U.  S.  DEPARTMENT  OF  AGRICULTURE 

WEATHER  BUREAU 


MONTHLY 


WEATHER 

SUPPLEMENT  No.  19 


REYIEW 


THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA 

By  Henry  J.  Cox,  Meteorologist 


APPENDIX: 

THERMAL  BELTS  FROM  THE  HORTICULTURAL  VIEWPOINT 

By  W.  N.  Hutt,  Former  State  Horticulturist 


Submitted  for  publication  February  7,  19 


2*rz 


WASHINGTON 

GOVERNMENT  PRINTING  OFFICE 
1923 


SUPPLEMENTS  T6  THE  MONTHLY  WEATHER  REVIEW. 

During  the  summer  of  1913  the  issue  of  the  system  of  publications  of  the  Department  of  Agriculture  was  changed 
and  simplified  so  as  to  eliminate  numerous  independent  series  of  Bureau  bulletins.  In  accordance  with  this  plan, 
among  other  changes,  the  series  of  quarto  bulletins — lettered  from  A  to  Z — and  the  octavo  bulletins — numbered 
from  1  to  44 — formerly  issued  by  the  U.  S.  Weather  Bureau  have  come  to  their  close. 

Contributions  to  meteorology  such  as  would  have  formed  bulletins  are  authorized  to  appear  hereafter  as  Supple¬ 
ments  of  the  Monthly  Weather  Review.  (Memorandum  from  the  Office  of  the  Assistant  Secretary,  May  18,  1914.) 

These  Supplements  comprise  those  more  voluminous  studies  which  appear  to  form  permanent  contributions  to 
the  science  of  meteorology  and  of  weather  forecasting,  as  well  as  important  communications  relating  to  the  other 
activities  of  the  U.  S.  Weather  Bureau.  They  appear  at  irregular  intervals  as  occasion  may  demand,  and  contain 
approximately  100  pages  of  text,  charts,  and  other  illustrations. 

Owing  to  necessary  economies  in  printing,  and  for  other  reasons,  the  edition  of  Supplements  is  much  smaller  than 
that  of  the  Monhly  Weather  Review.  Supplements  will  be  sent  free  of  charge  to  cooperating  meteorological 
services  and  institutions  and  to  individuals  and  organizations  cooperating  with  the  Bureau  in  the  researches  wnich 
form  the  subject  of  the  respective  supplements.  Additional  copies  of  this  Supplement  may  be  obtained  from  the 
Superintendent  of  Documents,  Washington,  D.  C.,  to  whom  remittances  should  be  made. 

The  price  of  this  Supplement  is  50  cents. 


ii 


TABLE  OF  CONTENTS. 


Acknowledgments . 

Introduction . 

Description  of  region . 

General  temperature  and  rainfall  conditions  in  region  as 

affected  by  elevation . 

Scheme  of  work  and  distribution  of  stations . 

Description  of  topography  of  the  individual  slopes  and 

exposure  of  the  instruments . 

Arrangement  of  tables . 

Physical  explanation  of  local  variation  in  temperature  in 

daytime  and  nighttime . 

Maximum  Temperature . 

Average  monthly  and  annual  maximum  temperature . 

Average  maxima  at  individual  slopes;  also  maxima  during 

sunshiny  periods . 

Variations  in  maximum  temperature  in  clear  and  cloudy 

weather . . 

Rates  of  decrease  in  monthly  and  annual  average  maximum 

temperature  on  six  selected  long  slopes . 

Monthly  and  annual  average  maxima  at  the  two  stations 
having,  respectively,  the  highest  and  lowest  elevations. . 

Minimum  Temperature . 

Inversions  and  norms . 

Additional  types  of  inversions . 

Mountain  breezes . 

Average  monthly  and  annual  minimum  temperature . 

Average  minimum  temperature  on  individual  slopes;  also 

minima  during  periods  of  inversion  and  norm . 

Variation  in  minimum  temperature  during  periods  of 

inversion  in  spring  and  autumn . 

Rates  of  increase  or  decrease  in  average  monthly  and  annual 

minimum  temperature  on  six  selected  long  slopes . 

Monthly  and  annual  average  minima  at  the  two  stations 
having  the  highest  and  lowest  elevations,  respectively. . . . 

Norms . 

Absolute  Maximum  and  Absolute  Minimum  Tempera¬ 
tures . 

Range  in  Temperature . 

Absolute  range . 

Average  annual  range  in  temperature . 

Daily  range  and  seasonal  variation . 

Mean  Temperature . 

Monthly  and  annual  mean  temperatures . 

Rates  of  decrease  in  monthly  and  annual  mean  tempera¬ 
ture  on  six  selected  long  slopes . . 

Monthly  and  annual  mean  temperature  at  the  two  stations 
having,  respectively,  the  highest  and  lowest  elevations .  . 


Page.  Pagei 

1  Inversions .  55 

2  /  Topographical  and  meteorological  factors  in  inversions .  55 

2  Selected  months  of  inversions  on  the  long  slope  at  Ellijay 

and  on  the  short  slope  at  Highlands .  55 

3  Inversions  on  six  selected  long  slopes  having  a  vertical 

4  height  of  1,000  feet  or  more .  58 

Inversions  on  six  selected  short  slopes .  59 

5  Inversions  of  stated  amounts  on  six  selected  long  slopes  in 

21  the  year  1914 .  60 

Inversions  of  stated  amounts  on  six  selected  short  slopes  in 

21  1  the  year  1914 .  63 

23  ’•Effects  of  variation  in  vapor  pressure,  relative  humidity, 

25  j  and  temperature  upon  degree  of  inversion .  64 

’Effect  of  wind  direction  and  velocity  upon  degree  of  inver- 

26  /  sion .  66 

*  Effect  of  variation  of  soil  cover  upon  degree  of  inversion. .  67 

32  Inversions  on  individual  slopes  as  affected  by  topography. .  67 

Isopleths  showing  progressive  distribution  of  temperature 

33  during  a  May  period  of  inversion  at  Ellijay .  75 

Mean  minimum  temperatures  during  inversion  weather  at 

33,  14  base  stations  corrected  for  latitude  and  to  the  2,000-foot 

level .  75 

34  Approximate  vertical  temperature  gradients  during  typical 

34  periods  of  inversion .  77 

34  Height  of  Thermal  Belt .  78 

34  |  Average  position  of  the  center  of  thermal  belt  od  nights  of 

36  ^Seasonal  fluctuation  of  the  thermal  belt .  79 

Top  Freezes  and  Norms .  80 

43  Norms  on  selected  long  slopes  having  a  vertical  height  of 

1,000  feet  or  more .  81 

44  Isopleths  showing  progressive  distribution  of  temperature 

at  Ellijay  during  a  December  period .  83 

45  \  Hour-Degrees  of  Frost .  84 

45  \ Verdant  Zones .  87 

Rise  in  temperature  at  summit  stations  earlier  than  on  the 

46  valley  floor .  89 

49  Dew  point  and  ensuing  minimum  temperature .  90 

49  Length  of  growing  season . _ .  92 

50  Fruit  growing  iD  the  Carolina  mountain  region  and  percent- 

50  age  of  crops,  1913-1916 .  95 

52  Fruit  growing  at  high  elevations  in  the  West .  97 

52  Conclusion .  97 


53 

54 


APPENDIX. 


Page. 


Thermal  belts  from  the  horticultural  viewpoint .  99 

Late  blooming  varieties .  102 

Fruit  report  for  1914 .  102 

Fruit  crop  report  for  1915 .  103 

The  danger  period  of  1916 .  104 


Page. 

Thermal  belts  from  the  horticultural  viewpoint — Continued. 


Frost  pockets .  105 

Conclusions .  106 

Selected  bibliography .  106 


hi 


ILLUSTRATIONS. 


Page. 


Frontispiece. — Relief  map  of  western  North  Carolina . opp.  1 

Fig.  1.  — Average  annual  rainfall  and  temperature,  western 

North  Carolina,  1913-1916 .  3 

Fig.  2.  — Bryson,  Contour  map  and  profile .  6 

Fig.  3.  — Eliijay,  contour  map  and  profile .  7 

Fig.  4. — Station  No.  5,  Eliijay . opp.  6 

Fig.  5 — Slope  north  side  Eliijay  creek  facing  research  stations 

showing  snow  line  April  9,  1916 . opp.  7 

Fig.  6.  — Highlands,  contour  map  and  profile .  8 

Fig.  7. —Cooperative  Weather  Bureau  staton,  Rock  House,  N. 

C.  (near  Highlands) . opp.  7 

Fig.  8.  — Station.  3,  Highlands,  coldest  of  all  stations . opp.  7 

Fig.  9. — Blantyre,  contour  map  and  profile .  9 

Fig.  10.  — Station  No.  1,  Blantyre,  on  State  farm  directly  below  a 

northeast  slope  of  French  Broad  River . opp.  7 

Fig.  11. — Station  No.  2,  Blantyre,  on  State  farm  in  sag  at  base 

of  Little  Fodderstack  Mountain . opp.  7 

Fig.  12.  — Stations  Nos.  3  and  4,  Blantyre,  in  orchard  of  State  farm 

Little  Fodderstack  Mountain . opp.  7 

Fig.  13.  — Hendersonville,  contour  map  and  profile .  10 

Fig.  14. — Station  No.  1,  Hendersonville . opp.  7 

Fig.  15. — Station  No.  2,  Hendersonville . opp.  7 

Fig.  16.  — Station  No.  3,  Hendersonville . opp.  7 

Fig.  17.  — Asheville,  contour  map  and  profile . . .  11 

Fig.  18.  — North  slope  in  orchard  near  Asheville,  looking  down 

valley . opp.  7 

Fig.  19.  — Northerly  slope  of  orchard,  in  which  stations  Nos.  2 

and  3  are  located . opp.  7 

Fig.  20. —Southerly  slope  opposite  orchard,  Station  No.  2a,  in 

center;  Station  No.  3a  above  No.  2a  obscured  by  timber . opp.  7 

Fig.  21.  — Tryon,  contour  map  and  profile .  12 

Fig.  22.  — Station  No.  1,  Tryon,  on  valley  floor,  Pacolet  River — ■ 

Warrior  Mountain  in  background . opp.  7 

Fig.  23.  — Warrior  Mountain,  Tryon,  showing  location  of  stations 

Nos.  2,  3,  and  4 . •. . opp.  7 

Fig.  24.  —Station  No.  3,  Tryon,  on  slope  above  vineyard . opp.  7 

Fig.  25.  — Cane  River,  contour  map  and  profile .  13 

Fig.  26.  — Altapass,  contour  map  and  profile .  14 

Fig.  27. — Station  No.  2,  Altapass,  photographed  February  28, 

1916 . opp.  7 

Fig.  28.  — Station  No.  4,  Altapass,  orchard  on  steep  slope . opp.  7 

Fig  29.  — Station  No.  5  Altapass,  on  grass  plot  on  summit,  orchard 

on  left  and  below . opp.  7 

Fig.  30.  — Blowing  Rock,  contour  map  and  profile .  15 

Fig.  31.  — Grandfather  Mountain  from  Blowing  Rock . opp.  7 

Fig.  32.  — Flat  Top  Orchard,  Blowing  Rock,  stations  3,  4,  and  5.  opp.  7 
Fig.  33.  ■ — Portion  Flat  Top  Orchard  from  station  No.  4,  Blowing 
Rock.  Looking  southeast  small  lake  in  foreground,  above 

which  is  station  No.  3 . opp.  7 

Fig.  34.  — South  slope  of  orchard  at  Valle  Crucis,  near  Blowing 

Rock . opp.  7 

Fig.  35.  — Globe,  contour  map  and  profile .  16 

Fig.  36.  — Gorge,  contour  map  and  profile .  17 

Fig.  37.  — Transon,  contour  map  and  profile .  18 

Fig.  38. — Wilkesboro,  contour  map  and  profile . .  19 

Fig.  39.  —Mount  Airy,  contour  map  and  profile .  20 

Fig.  40.  — Sparger  Orchard,  Mount  Airy,  station  No.  1  on  extreme 

left . . . opp.  7 

Fig.  41.  — Sparger  Orchard,  Station  No.  4,  Mount  Airy  in  center,  opp.  7 
Fig.  42. — Effect  of  varying  inclination  and  direction  of  slopes 

upon  maximum  temperatures .  26 

Fig.  43.  — Thermograph  traces,  north-and-south-facing  slopes, 
October  30— November  1,  1913,  Asheville:  Stations  2  and  3, 
and  2a  and  3a  are  located  on  opposite  slopes  facing  north  and 

south,  respectively . 27 

Fig.  44.  Thermograph  traces,  January  4-5,  1916,  Stations  Nos.  1, 

3,  and  4,  Cane  River .  29 


Fig.  45.  — Average  daily  maxima  during  selected  period  of  clear 
weather  in  spring;  stations  grouped  according  to  elevation 
above  sea  level .  33 


Page. 


Fig.  46.  — Average  daily  maxima  during  selected  period  of  clear 
weather  in  autumn;  stations  grouped  according  to  elevation 

above  sea  level . . .  33 

Fig.  47.— Average  daily  minima  during  selected  inversion 
periods  in  spring:  stations  grouped  according  to  elevation 

above  sea  level .  35 

Fig.  48  — Average  daily  minima  during  selected  inversion  period 
in  autumn;  stations  grouped  according  to  elevation  above  sea 

level .  35 

Fig.  49. — Average  daily  minima  during  eight  selected  norm 
nights  in  January,  February,  and  March,  1916;  stations  grouped 

according  to  elevation  above  sea  level .  46 

Fig.  50. — Absolute  and  average  annual  maximum  and  minimum 
temperatures  and  range,  six  long  slopes;  solid  lines  show 

extremes;  shaded,  averages . 50 

Fig.  51. — Average  daily  range  in  temperature,  six  longslopes _  51 

Fig.  52. — Monthly  frequency,  average  and  extreme  degrees  of 

inversion  on  five  selected  long  slopes .  59 

Fig.  53. — Relation  of  degree  of  inversion  to  variation  in  vapor 

pressure  and  relative  humidity .  64 

Fig.  54. — Thermograph  traces,  January  3-5,  1916,  stations  Nos. 

1  and  5,  Altapass,  showing  importation  of  warm  air  at  summit. .  68 

Fig.  55.- — Thermograph  traces,  May  2-3,  1913,  north  and  south 

facing  slopes,  Asheville .  68 

Fig.  56. — Thermograph  traces,  November  12-14,  1913,  stations 

Nos.  1,  2,  3  and  4,  Blantyre;  large  inversions. . .  68 

Fig.  57. — Thermograph  traces,  November  1-5,  1916,  stations 

Nos.  1,  2,  3,  and  5,  Blowing  Rock .  69 

Fig.  58.— Thermograph  traces,  January  27-29,  1914,  stations 

Nos.  1  and  4,  Cane  River,  large  inversion .  70 

Fig.  59. — Thermograph  traces,  December  19-23,  1916,  stations 

Nos.  1  and  4,  Cane  River .  71 

Fig.  60. — Thermograph  traces,  November  2-5, 1916,  and  Novem¬ 
ber  19-21,  1913,  stations  Nos.  1,  2,  and  4,  Hendersonville .  72 

Fig.  61. — Thermograph  traces,  October  11-12, 1916,  stations  Nos. 

2  and  3,  Mount  Airy;  variation  in  minimum  temperature  due 

to  inclination  of  slope .  73 

Fig.  62. — Thermograph  traces,  October  28-31, 1914,  stations  Nos. 

1,  2,  and  4,  Tryon .  73 

Fig.  63.— Vertical  temperature  gradients  under  varying  condi¬ 
tions,  October  29-31,  1914,  Tryon .  74 

Fig.  64. — Isopleths,  selected  inversion  period,  May,  1914,  Eliijay.  75 
Fig.  65. — Approximate  free  air  temperature  gradients  over 
western  North  Carolina  during  periods  of  inversion  in  spring 

and  fall .  77 

Fig.  66. — Average  position  of  thermal  belt  on  six  long  slopes, 

during  typical  inversion  weather .  78 

Fig.  67. — Monthly  frequency  and  average  and  extreme  degrees 

of  norm  on  six  long  slopes .  83 

Fig.  68. — Isopleths  and  thermograph  traces,  selected  period 

December,  1916,  Eliijay .  83 

Fig.  69. — Thermograph  traces,  March  2-4,  1916,  stations  Nos.  1 

and  5,  Altapass,  and  stations  Nos.  1  and  5,  Eliijay .  84 

Fig.  70. — Average  number  hour-degrees  of  frost,  10  selected  in¬ 
versions  .  86 

Fig.  71. — Average  number  hour-degrees  of  frost,  10  selected  norms  86 

Fig.  72. — Average  total  number  hour-degrees  of  frost,  10  selected  • 

inversions  and  10  selected  norms .  87 

Fig.  73. — Thermograph  traces  and  vertical  temperature  grad¬ 
ients,  April  8-10,  1916,  stations  Nos.  1,  2,  and  4,  Tryon .  87 

Fig.  74. — Possible  variation  in  limits  of  verdant  zone  on  moun¬ 
tain  slopes .  88 

Fig.  75. — Thermograph  traces,  November  12-13,  1913,  stations 

Nos.  1  and  5,  Gorge .  89 

Fig.  76. — Average  monthly  difference  between  evening  dew¬ 
point  and  ensuing  minimum  temperature .  91 

Fig.  77. — Length  of  growing  season .  92 

Fig.  78.— Length  of  growing  season ;  stations  grouped  according 
to  elevation  above  sea  level .  93 


IV 


LIST  OF  TABLES. 


Page. 


1.  — Monthly  and  annual  average  maximum  temperatures .  23 

la.  — Average  maximum  temperatures  during  selected  clear 

periods . . .  24 

lb.  — Average  differences  between  the  maximum  temperatures 

on  the  three  long  slopes  of  Altapass,  Ellijay,  and  Gorge  on 
selected  days  of  cloudy  weather,  showing  the  rate  of  decrease 
with  elevation .  25 

lc.  — Rate  of  decrease  in  monthly  and  annual  average  maximum 

temperatures  on  six  selected  long  slopes .  25 

ld.  — Monthly  and  annual  average  maximum  temperatures  at 

the  two  stations  having  the  highest  and  lowest  elevation 
respectively  with  rates  of  decrease  in  elevation .  25 

2.  — Monthly  and  annual  average  minimum  temperatures .  35 

2a. — Average  minimum  temperatures  during  selected  inversion 

and  norm  periods .  37 

2b. — Rate  of  increase  or  decrease  in  monthly  and  annual  average 
minimum  temperatures  on  six  selected  long  slopes .  44 

2c. — Monthly  and  annual  average  minimum  temperatures  at 
the  two  stations  having  respectively,  the  highest  and  lowest 
elevations  with  rate  of  decrease  in  elevation .  45 

3.  — Absolute  annual  maximum  and  minimum  temperatures  and 

range . 48 

4.  — Monthly  and  annual  mean  temperatures .  52 

4a. — Rate  of  decrease  in  monthly  and  annual  mean  tempera¬ 
tures  on  six  selected  long  slopes .  54 

4b. — Monthly  and  annual  mean  temperatures  at  the  two  stations 
having  the  highest  and  lowest  elevations  with  rate  of  decrease 
with  elevation .  54 

5.  — Monthly  record  of  minimum  temperatures  and  differences, 

May,  1914,  Ellijay .  56 

6.  — Monthly  record  of  minimum  temperatures  and  differences, 

May,  1914,  Highlands .  57 

7.  — Monthly  record  of  minimum  temperatures  and  differences, 

November,  1914,  Ellijay .  57 


Page. 


8.  — Monthly  record  of  minimum  temperatures  and  differences, 

November,  1914,  Highlands .  57 

9.  — Monthly  record  of  minimum  temperatures  and  differences, 

July,  1916,  Ellijay .  57 

10.  — Monthly  record  of  minimum  temperatures  and  differences, 

July,  1915,  Ellijay .  58 

11.  — Monthly  record  of  minimum  temperatures  and  differences, 

January,  1916,  Ellijay .  58 

12. — Monthly  record  of  minimum  temperatures  and  differences, 

February,  1915,  Ellijay .  58 

13.  — Total  monthly  and  annual  number  of  inversions  of  5°  or 

more  on  six  long  slopes,  1913-1916 .  60 

14.  — Total  monthly  and  annual  number  of  inversions  of  5°  or 

more  on  six  short  slopes,  1913-1916 .  61 

15.  — Total  monthly  and  annual  number  of  inversions  of  5°,  10°, 

15°,  and  20°  on  six  long  slopes,  1914 .  62 

16.  — Total  monthly  and  annual  number  of  inversions  of  5°,  10°, 

15°,  and  207  on  six  short  slopes .  63 

17.  — Average  hourly  temperature  during  clear  humid  and  clear 

dry  weather,  Ellijay .  65 

18. — Effect  of  wind  direction  and  velocity  on  inversions .  67 

19.  — Average  minimum  temperatures  during  inversion  weather 

at  14  base  stations,  corrected  for  latitude  and  to  the  2,000-foot 
level .  76 

20.  — Seasonal  fluctuation  of  the  thermal  belt .  80 

21.  — Monthly  record  of  minimum  temperatures  March,  1916, 

Ellijay .  81 

22.  — Total  monthly  and  annual  number  of  norms  of  5°  or  more 

on  six  long  slopes . 82 

23.  — Rises  in  temperature  at  summit  stations .  90 

24.  — Length  of  growing  season .  94 

25.  — Length  of  growing  season  and  number  of  hour-degrees  of 

frost  combined .  96 


APPENDIX. 


Page. 


1.  Summary  of  horticultural  data  for  season  of  1913 . -  100 

2.  Temperatures  at  different  slope  stations,  freeze  of  April 

22-23,1913 .  . .  100 

3.  Temperatures  at  different  stations  in  cold  spell  of  May  11-12, 

1913 .  101 


Page. 


4.  Summary  of  horticultural  data  for  season  of  1914 .  103 

5.  Summary  of  horticultural  data  for  season  of  1915 .  103 

6.  Minimum  temperatures  at  different  stations  March  16,  1916. .  104 

7.  Summary  of  horticultural  data  for  season  of  1916 .  105 


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THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA 

Henry  J.  Cox,  Meteorologist. 

ACKNOWLEDGMENTS. 


Acknowledgment  is  made  of  the  assistance  of  Prof. 
Charles-  F.  Marvin,  Chief,  U.  S.  Weather  Bureau,  who  in 
his  former  position  in  charge  of  the  Instrument  Di¬ 
vision,  cooperated  to  the  fullest  extent  in  supplying  in¬ 
strumental  equipment  for  the  observations,  and  who  later 
advised  as  to  the  scope  of  the  research  and  reviewed  the 
manuscript,  offering  many  helpful  suggestions.  Ac¬ 
knowledgment  is  made  to  Prof.  A.  J.  Henry,  U.  S. 
Weather  Bureau,  who  reviewed  and  edited  the  manuscript 
and  gave  much  time  to  an  examination  of  the  tables, 
maps,  and  graphs. 

The  assistance  of  those  who  have  taken  part  in  this 
investigation  is  also  hereby  acknowledged:  Mr.  E.  IP. 
Haines,  U.  S.  Weather  Bureau,  performed  the  work  in 
the  field  and  assisted  in  the  compilations  and  in  the 
preparation  and  discussion  of  the  material;  Mr.  W.  P. 
Day,  U.  S.  Weather  Bureau,  prepared  the  illustrations  and 
assisted  in  the  compilations  and  in  the  preparation  and 


discussion  of  the  material;  Mr.  L.  A.  Denson,  U.  S. 
Weather  Bureau,  made  the  installations  of  the  stations 
and  gave  personal  attention  to  the  instrumental  equip¬ 
ment  during  the  period  of  the  research;  Mr.  W.  M.  IPutt, 
formerly  State  Horticulturist,  North  Carolina,  offered 
suggestions  and  advice,  with  special  reference  to  the 
horticultural  side  of  the  research;  Mr.  F.  R.  Baker, 
Drainage  Engineer,  North  Carolina  Department  of  Agri¬ 
culture,  made  surveys  of  the  slopes  upon  which  the  ex¬ 
perimental  stations  were  located  and  prepared  the  original 
topographical  maps.  Acknowledgment  is  also  made  of 
the  courtesies  extended  by  the  owners  of  the  various 
orchards  or  other  properties  in  which  the  experimental 
stations  were  operated  and  of  the  cooperation  of  the  in¬ 
dividual  observers. 

A  vast  amount  of  tabulated  data  has  been  prepared, 
but  the  number  of  tables  published  has  necessarily  been 
greatly  reduced  for  want  of  space. 


1 


INTRODUCTION. 


A  research  (upon  the  thermal  conditions  in  the  North 
Carolina  mountain  region)  was  inaugurated  in  1912  by 
the  United  States  Weather  Bureau  at  the  request  of  the 
North  Carolina  State  Board  of  Agriculture  and  the  State 
Horticulturist,  with  a  hope  that  the  so-called  Thermal 
Belts  might  be  more  clearly  defined,  and  that  safe  eleva¬ 
tions  in  the  various  sections  for  the  planting  of  fruit 
trees  might  be  determined,  as  far  as  possible. 

Considerable  success  had  been  obtained  in  many  por¬ 
tions  of  that  region  in  the  growing  of  hardy  fruit,  es¬ 
pecially  apples,  but  here  and  there  marked  failures  had 
occurred,  supposedly  because  either  of  too  great  altitude 
or  of  unfavorable  topography,  inducing  freezes  in  the  one 
case  and  severe  frosts  m  the  other. 

Heretofore  the  planting  of  orchards  in  the  mountain 
region  had  been  carried  on  in  a  rather  haphazard  way, 
so  far  as  the  influence  of  temperature  conditions  was  con¬ 
cerned,  and  it  was  believed  by  the  State  Horticulturist 
that  an  exhaustive  study  of  the  various  problems  might 
furnish  valuable  information  for  the  guidance  of  or- 
chardists  in  the  development  of  their  properties. 

The  special  meteorological  stations  that  were  estab¬ 
lished  in  the  North  Carolina  mountain  region  for  the 
purpose  of  this  study  at  points  shown  in  relief  map  in 
frontispiece  were  conducted  under  the  direction  of  the 
Weather  Bureau,'  while  the  State  Horticulturist  has 
afforded  assistance  with  advice  and  suggestions. 

Reference  has  frequently  been  made  in  meteorological 
and  climatological  literature  to  thermal  belts  or 
frostless  zones  in  mountain  districts,  both  in  this  country 
and  in  Europe.  These  belts,  of  varying  width  in  which 
frost  is  never  observed,  were  said  to  be  found  on  certain 
slopes  between  the  valley  floor  and  the  summit,  their 
development  being  mainly  due  to  the  fact  that  during 
certain  cool  nights  the  temperature  is  relatively  high  on  the 
slope — much  higher  than  at  the  base. 

This  phenomenon,  termed  the  inversion  of  temperature, 
is  observed  most  frequently  on  clear,  quiet  nights,  but 
somefctimes  on  partly  cloudy  and  even  cloudy  nights.  It 
is  called  an  "in version”  because  ordinarily  we  expect  a 
fall  in  temperature  with  elevation,  which,  for  the  want  of 
a  better  name,  we  may  here  term  a  “norm”  in  contrast 
with  the  term  “inversion.  ”  On  the  average  the  tempera¬ 
ture  of  the  free  air  falls  with  height,  the  mean  rate  of 
decrease  being  1°  F.  in  300  feet  of  ascent,  and  there  are 
many  nights  in  the  mountain  region  when  this  decrease 
in  temperature  with  elevation  or  even  a  greater  one  is 
observed,  especially  when  the  weather  is  cloudy  and 
windy.  There  are  still  other  nights,  moist  and  damp, 
when  the  differences  in  temperature  between  various  ele¬ 
vations  are  hardly  appreciable. 

Both  inversions  and  norms  prevail  within  mountain 
valleys  to  a  considerable  vertical  height,  and  are  important 
factors  in  the  question  of  fruit  growing.  In  the  one  case 
the  minumum  temperature  is  lowest  at  the  base  and  high¬ 
est  at  some  point  on  the  slope  or  at  the  summit,  while  in 
the  other  case  the  minimum  is  lowest  at  the  summit  and 
highest  at  the  base;  and,  through  a  combination  of  these 
two  conditions,  we  sometimes  have  a  belt  more  or  less 
indefinite  in  width  where  the  minima  average  higher  than 
2 


at  either  the  base  or  the  summit,  free  from  the  frosts  of  the 
valley  and  from  the  freezes  of  the  higher  levels.  Within 
this  belt,  which  might  properly  be  called  a  “verdant 
zone,”  the  foliage  is  fresh  and  green  as  compared  with 
that  above  and  below. 

DESCRIPTION  OF  REGION. 

More  has  probably  been  written  regarding  thermal  belts 
in  the  North  Carolina  mountains  than  in  any  other 
section  of  the  country,  doubtless  because  the  phenomena 
are  more  pronounced  there  than  elsewhere  in  the  East  on 
account  of  the  more  extensive  slopes  and  the  greater  area. 
The  Appalachian  Mountains,  which  form  the  divide  be¬ 
tween  the  great  central  valleys  of  theUnited  States  and  the 
Atlantic  Plain,  extend  in  a  southwest-northeast  direction 
from  Pennsylvania  to  northwest  Georgia,  but  the  cul¬ 
minating  section  of  the  system  lies  in  western  North 
Carolina.  While  the  elevation  of  the  Atlantic  Plain  at 
the  base  of  the  mountains  is  only  150  feet  in  Pennsylvania, 
and  perhaps  500  feet  in  Virginia,  in  North  Carolina  it 
rises  to  about  1,000  feet. 

The  Appalachians  divide  into  two  chains  in  Virginia, 
one  known  as  the  Great  Smokies,  continuing  in  its  south¬ 
westerly  course  and  forming  the  boundary  of  western 
North  Carolina,  and  the  other,  retaining  the  name  of 
the  Blue  Ridge,  as  the  range  in  the  north  is  called, 
crossing  the  State  farther  eastward  and  forming  the 
great  watershed  of  the  drainage  of  that  section.  Be¬ 
tween  the  two  chains  lies  a  remarkable  region  of  valleys 
and  plateaus,  at  no  point  falling  to  a  lower  elevation  than 
2,000  feet,  while  portions  of  the  plateau  in  Watauga 
County  to  the  north  and  Macon  County  to  the  south 
have  elevations  ranging  from  3,500  to  4,000  feet.  Within 
this  system  scores  of  mountain  peaks  rise  to  an  altitude 
of  more  than  5,000  feet,  and  many  even  more  than  6,000 
feet,  Mount  Mitchell  being  the  highest,  with  an  elevation 
of  6,711  feet. 

The  North  Carolina  mountain  region,  then,  is  preemi¬ 
nently  a  land  of  high  mountains  and  plateaus,  and  because 
of  its  elevation  it  is  known  as  the  “Land  of  the  Sky,” 
a  region  most  irregular  in  shape,  having  an  area  of  over 
5,000  square  miles  and  extending  in  a  northeast-south¬ 
west  direction,  about  125  miles. 

In  a  general  view  the  eastern  chain,  or  Blue  Ridge,  is 
seen  to  be  irregular  and  fragmentary,  while  the  western 
chain,  the  Great  Smokies,  is  more  regular,  elevated,  and 
continuous.  Nevertheless,  the  drainage  of  the  plateau 
between  the  two  is  thrown  entirely  to  the  westward. 
Numerous  cross  chains  uniting  the  main  ranges  form 
basins  which  contain  the  mountain  tributaries  of  the 
Tennessee  River.  Projecting  into  the  Piedmont  region 
east  of  the  Blue  Ridge  are  a  few  detached  chains  and 
isolated  knobs. 

The  principal  streams  of  the  mountain  region  rise  in  the 
Blue  Ridge,  and  those  trending  westward  break  through 
the  more  elevated  western  barrier  in  deep  chasms,  the 
French  Broad,  the  North  Toe,  and  the  Pigeon,  all  three 
flowing  into  the  Tennessee;  and  the  Tuckasegee,  into  the 
Little  Tennessee;  while  those  on  the  other  side  of  the 


THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 


ridge  trending  eastward  are  the  Yadkin,  emptying  into 
Ree  Pee  River?  and  the  Catawaba,  separated  from 
the  i  adkin  by  the  Brushy  Mountains  and  flowing  first 
easterly  and  then  southerly  through  the  Piedmont 
region  into  the  Atlantic. 

.  The  mountains  are  for  the  most  part  covered  with 
timber  up  to  their  very  summits,  even  Mount  Mitchell 
having  considerable  forest  growth  at  the  highest  points; 
but  there  are  a  few  peaks,  termed  “  Balds, with  eleva¬ 
tions  of  5,000  feet  or  more,  whose  rounded  knobs  are 
almost  bare  of  timber. 

The  relief  map  in  the  frontispiece  shows  the  general 
topography  of  the  region. 


GENERAL  TEMPERATURE  AND  RAINFALL  CONDITIONS  IN 
REGION  AS  AFFECTED  BY  ELEVATION. 

The  modifying  effect  of  elevation  on  the  general 
meteorological  conditions  of  the  region  is  twofold — viz, 
a  reduction  in  temperature  and  an  increase  in  rainfall. 
The  isotherms  as  they  approach  from  the  eastern  low¬ 
lands  curve  southward  rapidly  and,  after  crossing  the 
mountains  more  or  less  irregularly  at  right  angles,  bend 
sharply  northward,  while  the  rainfall  is  much  greater 
in  the  mountain  region  than  at  the  lower  levels,  and  is 
greatest  over  the  more  elevated  sections,  especially 
those  on  the  side  of  the  mountains  facing  the  rain¬ 
bearing  winds. 

Figure  1  gives  the  average  annual  percipitation  over 
western  North  Carolina  for  the  four  years  1913^1916. 
Isotherms  for  the  same  period  are  also  shown  and  in  the 
upper  left-hand  corner  will  be  found  a  key  to  the  loca¬ 
tion  of  the  observing  stations,  also  the  mean  annual 


temperature  and  elevation  above  mean  sea  level  of  the 
base  stations. 

Taking  temperature  conditions  in  the  sections  to 
the  east  of  the  mountains  as  a  basis,  there  is  normally, 
because  of  the  difference  in  latitude,  about  2°  difference 
in  the  mean  annual  temperature  between  the  northern 
and  southern  limits  of  this  mountain  region.  In  the 
lower  levels  the  isotherm  of  59°  F  1  runs  somewhat  south 
of  the  Virginia-North  Carolina  border,  while  that  of  61° 
is  approximately  in  line  with  the  Georgia-North  Carolina 
boundary.  Temperature  data  for  the  summits  of  the 
highest  mountains  in  North  Carolina  are  not  available, 
but  the  means  deduced  from  the  observations  at  places 


having  altitudes  up  to  4,000  feet  are  sufficient  to  show 
strikingly  the  effect  of  elevation  upon  temperature.  The 
lowest  annual  mean  for  a  considerable  period  in  the 
mountain  region  is  49°  at  Blowing  Rock  and  Highlands, 
both  about  3,600  feet  above  sea  level,  the  first  in  the 
extreme  northwestern  portion  and  the  other  in  the 
extreme  southwestern  portion  of  the  State.  Because  of 
the  difference  in  latitude,  Blowing  Rock  should  nor¬ 
mally  average  2°  colder  than  Highlands,  but  this  varia¬ 
tion  is  not  apparent  in  the  observations  because  of  the 
difference  in  topography,  the  station  at  the  latter  place 
being  located  in  a  well-marked  frost  pocket  where  the 
night  temperature  averages  uniformly  low.  This  mean 
annual  temperature  of  49°  is  approximately  the  mean 
of  .the  Weather  Bureau  station  at  Albany,  N.  Y.,  where 
the  thermometer  shelter  stands  about  100  feet  above 
sea  level. 


1  Fahrenheit  degrees  and  English  units  are  used  throughout  this  discussion. 


Meon  Annuo!  Temperature 

v?7->»7-/o-v  CLCVAT/O/V 

(/)  T ft  YON  930 

GORGE 
©  GLOBE 
®  BRYSON 
©  BLANTYRE 
©  /-iENDERSONY/LLB 
@  ALTARASS*  t 
@  ELUJA  Y 
0  ASH3Y/LL3. 


Fig.  1.— Average  annual  rainfall  and  temperature,  western  North  Carolina,  1913-16. 


4 


SUPPLEMENT  NO.  19. 


The  rainfall  in  the  Carolina  mountain  region,  as  shown 
in  Figure  1,  varies  considerably  and  it  is  generally  much 
heavier  than  on  the  Atlantic  Plain.  The  largest  amounts 
occur  along  the  main  Blue  Ridge,  especially  on  its  south¬ 
ern  and  eastern  sides,  as  the  principal  rain-bearing  winds 
in  that  section  are  from  east  to  south.  The  southerly 
winds  carry  the  moisture-laden  air  from  the  Atlantic  and 
the  Gulf  of  Mexico,  and  naturally  the  greatest  rainfall  is 
recorded  at  the  stations  farthest  to  the  south,  where 
these  east  to  south  winds,  moving  inland,  pass  upward 
over  the  slopes,  the  cooling  of  the  air  resulting  in  con¬ 
densation,  often  excessive.  During  a  four-year  period, 
1913-1916,  inclusive,  the  gauge  at  Highlands  registered  an 
average  annual  precipitation  of  97.86  inches,  the  total  in 
1915  being  111.21  inches,  and  in  1916,  105.10  inches, 
two  extremely  wet  years.  In  the  same  period  the  cooper¬ 
ative  station  at  Rock  House,  formerly  known  as  Horse 
Cove,  (Fig.  7),  about  six  miles  southeast  of  Highlands, 
recorded  an  average  rainfall  of  94.62  inches.  These 
figures  are  considerably  above  the  average  for  a  long 
eriod  of  years,  which  are,  respectively,  80  and  82  inches, 
ut  in  any  case  this  spot  in  the  mountain  region  close  to 
the  North  Carolina-Georgia  boundary  is  the  wettest 
place  in  the  United  States  except  the  extreme  northwest 
racific  coast. 

The  rainfall  over  the  Great  Smokies  is  much  less  than 
along  the  Blue  Ridge,  because  the  southerly  and  easterly 
rain-bearing  winds  are  shut  off,  or  at  least  their  moisture 
is  largely  condensed  over  the  Blue  Ridge  before  reaching 
the  Smokies.  Moreover,  the  rainfall  on  the  plateau  in¬ 
closed  by  these  two  mountain  ranges  is  very  much  less 
than  on  the  surrounding  mountains,  obviously  because 
of  the  condensation  of  alarge  portion  of  the  moisture  at 
the  higher  levels  before  the  winds  reach  the  plateau. 
Asheville,  in  the  valley  of  the  French  Broad  River  and 
walled  in  by  mountains  has  an  average  annual  rainfall 
of  only  39  inches. 

SCHEME  OF  WORK  AND  DISTRIBUTION  OF  STATIONS. 

Although  the  special  research  was  inaugurated  in  1912, 
it  was  not  until  the  first  part  of  1913  that  all  the  stations 
selected  were  in  full  operation.  Stations  were  installed 
at  16  places  in  the  mountain  region,  Bryson,  Ellijay, 
Highlands,  Waynesville,  Blantyre,  Hendersonville,  Ashe¬ 
ville,  Tryon,  Cane  River,  Altapass,  Blowing  Rock,  Globe, 
Gorge,  Transon,  Wilkesboro,  and  Mount  Airy.  Bryson  is 
the  most  westerly,  Mount  Airy,  close  to  the  Virginia  border, 
the  most  northerly  and  easterly,  and  Highlands  and 
Tryon,  close  to  the  Georgia  and  South  Carolina  borders, 
respectively,  the  most  southerly.  At  the  16  points  of 
of  observation  there  was  a  total  of  68  stations,  varying 
at  each  point  from  3  to  5.  The  point  having  the  greatest 
elevation  is  Highlands,  where  the  stations  range  from 
3,350  feet  to  4,075  feet  in  altitude,  and  the  lowest  is 
Tryon,  its  base  station  having  an  altitude  of  only  950  feet. 
Six  of  the  slopes,  Ellijay,  Tryon,  Cane  River,  Altapass, 
Globe,  and  Gorge,  have  differences  in  elevation  between 
base  and  summit  of  1,000  feet  or  more,  the  longest  slope, 
1,760  feet,  being  at  Ellijay.  Some  of  the  slopes  are  steep, 
and  others  are  gentle,  irregular,  and  broken  up  into  coves 
and  frost  pockets.  Some  are  heavily  timbered,  while 
others  are  comparatively  free  from  forest  growth,  just  as 
certain  of  the  individual  stations  are  surrounded  by  dense 
vegetation  while  others  are  more  or  less  bare. 

At  one  point,  Asheville,  the  stations  were  located  above 
a  valley  floor  on  two  slopes,  northerly  and  southerly, 
facing  each  other,  while  at  two  other  places,  Bryson  and 
Mount  Airy,  the  stations  were  on  slopes  leading  down 


from  different  sides  of  knobs.  Nearly  all  the  short 
slopes  lead  up  to  isolated  knobs,  also  some  of  the  longer 
ones,  and  in  other  cases  there  is  a  large  extent  of  surface 
area  near  the  summit.  Some  of  the  valleys  at  the  base  of 
the  slopes  are  narrow  and  confined,  and  others  are  com¬ 
paratively  broad ;  again,  some  base  stations  are  located  on 
broad  benches.  A  wide  range  of  conditions  has  thus  been 
afforded  for  investigation. 

The  places  were  fairly  well  distributed  geographically, 
all  being  located  in  the  main  portion  of  the  mountain 
district  with  the  exception  of  Wilkesboro  and  Mount 
Airy,  which  lie  in  the  foothills  to  the  east.  Two  places, 
Blowing  Rock  and  Altapass,  are  on  the  main  Blue  Ridge. 
There  was  no  definite  uniformity  observed  in  determining 
the  positions  of  the  stations  on  the  individual  slopes, 
the  exact  locations  in  some  cases  being  dependent  upon 
conditions  beyond  the  control  of  the  leader,  the  purpose 
being  to  place  at  least  one  or  two  stations  in  each  group 
within  an  orchard,  when  one  was  available. 

The  task  of  selecting  locations  for  the  stations  was 
rather  difficult.  The  purpose  was,  of  course,  to  make  as 
complete  a  survey  as  possible  of  the  meteorological  con¬ 
ditions  in  the  mountain  region.  The  scope  of  the  work, 
however,  had  its  limitations  because  of  the  difficulty  in 
securing  and  training  competent  observers  and  because 
of  the  impracticability  of  locating  stations  in  some  cases 
where  most  desired.  To  do  the  observation  work  with 
absolute  completeness,  experienced  observers  should  have 
been  located  at  many  elevated  points  well-nigh  inac¬ 
cessible;  but  this  was,  of  course,  impracticable.  The 
bureau  was  obliged  to  select  places  where  men  were 
available  to  take  observations,  generally  superintendents 
or  foremen  employed  in  the  orchards,  and  these  men  had 
to  be  trained  as  observers,  the  observation  work  being 
incidental  and  in  addition  to  their  regular  duties. 

The  places  selected  were  for  the  most  part  on  slopes 
having  orchards  already  planted,  the  number  of  stations 
at  each  place  averaging  four.  For  purposes  of  conven¬ 
ience  the  stations  were  numbered  in  consecutive  order 
from  the  base  to  the  summit,  station  No.  1  being  on  the 
valley  floor,  or  at  least  at  the  base  of  the  particular 
slope,  and  stations  Nos.  3,  4,  or  5,  as  the  case  might  be,  at 
the  summit,  or  as  far  up  as  practicable.  In  some  places, 
where  there  was  a  further  descent  below  the  base,  as  at 
Altapass,  the  No.  1  station  was  not  placed  actually  on 
the  valley  floor;  while  at  a  few  places,  as  at  Asheville, 
the  highest  station  was  not  at  the  summit,  the  location 
in  each  case  being  governed  by  the  exigency  of  the 
situation. 

The  observations  continued  at  all  16  places  until  the 
close  of  1916,  with  the  exception  of  Waynesville,  where 
the  work  was  terminated  in  the  middle  of  the  period. 
The  data  at  that  place,  on  account  of  this  interruption, 
have  consequently  not  been  included  herein.  For  the 
sake  of  uniformity  and  convenience,  the  dicussion  of  the 
observations  in  this  research  is  limited  to  the  four  years, 
1913-1916. 

The  individual  stations  were  furnished  with  ther¬ 
mometer  shelters  containing  thermographs  and  maxi¬ 
mum  and  minimum  thermometers,  these  instruments 
being  placed  about  5J  feet  above  the  ground;  and  one 
station  in  each  place,  called  the  “home  station,”  was 
supplied  with  a  mimimum  thermometer  attached  to  the 
outside  of  the  shelter,  a  sling  psychrometer,  and  a  rain 
gauge.  This  home  station  was  the  one  nearest  to  the 
residence  of  the  observer — at  some  places  at  the  base, 
at  others  on  the  slope  or  even  on  the  summit,  depending 
upon  the  convenience  of  the  particular  point  to  the 
observer’s  residence.  At  the  home  stations  the  observa- 


THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 


5 


tions  were  made  and  the  thermometers  set  daily,  while 
at  the  other  stations  the  readings  were  made  twice  a 
week  only,  the  thermograph  traces,  however,  furnishing  a 
continuous  record.  However,  the  data  at  the  home 
stations  are  more  complete  and  dependable  than  at  the 
others.  In  addition  to  the  instrumental  record  of  temper¬ 
ature  and  precipitation,  data  as  to  wind  direction  and 
estimated  velocity,  especially  at  sunrise  and  sunset,  and 
notes  as  to  the  character  of  the  weather  during  both  day 
and  night  were  kept  by  the  observers.  The  regular  equip¬ 
ment  at  Tyron  was  supplemented  by  a  hygrograph  at 
station  No.  3. 

There  were  not  available  at  any  of  the  special  stations 
instrumental  records  of  wind  or  sunshine,  but  the  records 
of  the  regular  Weather  Bureau  station  in  the  city  of 
Asheville  have  been  used  to  supplement  the  observations 
made  in  the  field.  Asheville  is  fortunately  located  in 
the  very  center  of  the  region  under  investigation,  and 
one  group  of  orchard  experimental  stations  was  estab¬ 
lished  a  few  miles  distant  from  the  city. 

Moreover,  the  observations  made  by  the  orchard  ob¬ 
servers  were  supplemented  in  the  spring  of  1916  by 
special  work  at  Ellijay,  Highlands,  Tryon,  and  Blowing 
Rock  by  Mr.  E.  H.  Haines,  of  the  Chicago  Weather  Of¬ 
fice,  and  in  the  spring  of  1915,  at  Ellijay  and  Highlands 
by  Prof.  H.  H.  Kimball  and  Mr.  R.  N.  Covert,  of  the 
Central  Office  at  Washington.  Professor  Kimball’s  ob¬ 
servations2  have  already  been  published. 

TOPOGRAPHY  OF  THE  INDIVIDUAL  SLOPES  AND  THE 
EXPOSURE  OF  THE  INSTRUMENTS. 

A  complete  description  of  the  conditions  under  which 
the  instruments  were  exposed  is  essential  to  an  under- 

*  Kimball,  H.  H.,  Nocturnal  Radiation  Measurement?,  Monthly  Weather  Review, 
February,  1918,  46 :  57-60. 


standing  of  the  observations,  and  detailed  statements 
regarding  the  environment  of  each  group  of  stations  will 
be  found  with  the  contour  maps  of  the  respective  stations. 
It  is  important  to  know  whether  the  slope  is  steep  or 
gentle,  whether  regular  or  broken  up  into  coves  and 
pockets;  also  its  height  above  the  base  and  above  sea 
level,  the  direction  of  its  inclination,  its  general  environ¬ 
ment  as  regards  topography  and  vegetation — in  a  word, 
to  know  every  condition  that  might  possibly  affect  the 
temperature,  rainfall,  humidity,  or  wind.  It  will  be 
found  later,  as  the  observations  are  discussed,  that 
exposure  and  environment  have  a  most  important  bear¬ 
ing  upon  the  situation. 

The  stations  are  not  located  necessarily  at  the  exact 
oints  where  the  numbers  appear  in  the  relief  map, 
ecause  these  numbers  are  entered  at  the  positions  of 
the  various  cities  or  villages,  while  in  many  instances 
the  experimental  stations  are  a  few  miles  distant.  This 
variation  will  be  explained  under  the  description  of  each 
group  of  stations,  and  the  special  contour  maps  and 
accompanying  profiles  will  show  in  detail  the  local  topog¬ 
raphy  at  each  place.  The  profiles  indicate  the  vertical 
distances  between  the  base  and  the  summit  stations  and 
the  vertical  and  horizontal  distances  from  station  to 
station.  As  stated  previously,  the  lowest,  or  base  sta¬ 
tion,  is  always  numbered  1,  while  the  highest  in  the 
group  has  been  numbered  3,  4,  or  5,  as  the  case  may  be, 
depending  upon  the  number  of  stations  employed. 

u  the  descriptions  of  the  stations  and  their  exposures, 
only  important  features  are  mentioned;  but  these,  at 
least,  are  necessary  to  an  understanding  of  the  observa¬ 
tions. 

The  shaded  portions  of  the  topographical  maps  indicate 
cleared  areas  in  the  vicinity  of  the  observation  stations. 

The  arrangement  of  the  stations  is  from  west  to  east, 
following  the  numbers  on  the  relief  map  which  forms  the 
frontispiece. 


SUPPLEMENT  NO.  19. 


BRYSON. 

Capt  A.  M.  Frye,  Observer.— A  group  of  four  stations  in  the  orchard 
of  the  observer,  about  2  miles  northeast  of  the  village  of  Bryson  and  U 
miles  (north  of  the  Tuckasegee  River,  on  the  valley  floor  of  Deep  Creek 
in  a  region  hemmed  in  on  the  north  by  the  spurs  and  ridges  of  the 


rated  from  station  No.  1  by  a  knob,  the  summit  of  which  is  about  400  feet 
southwest  of  station  No.  2.  No.  2a,  home  station,  on  south  slope  385 
feet  above  station  No.  1;  same  elevation  as  station  No.  2,  but  over  the 
hill  and  on  the  opposite  side;  shelter  in  midst  of  orchard  close  to  apple 
trees;  ascending  slope  on  all  sides,  except  gradually  descending  on 
south  side  between  two  hills;  timber  to  south  and  west  about  100  feet 


Fig. 


2. — Bryson,  contour  map  and  profile. 


Great  Smokies  and  on  the  south  by  the  Yalaka  Mountains;  mountains 
at  varying  distances  tower  above  on  nearly  all  sides.  Base  station,  No. 
1,  1,800  feet  above  sea  level,  in  a  grass  plot  on  a  flat  plain  with  the 
country  in  the  immediate  vicinity  rolling  and  broken.  Station  No.  2, 
in  a  cove  or  gully  385  feet  above  and  in  a  horizontal  direction  3,000  feet 
northeast  of  station  No.  1;  in  the  midst  of  apple  orchard,  the  trees 
being  a  few  feet  from  the  shelter  on  all  sides;  on  northerly  slope  sepa- 


distant.  Station  No.  3  on  a  small  knob  5?0  feet  above  station  No.  1; 
not  in  orchard;  shelter  surrounded  by  ferns  and  scrub  oaks;  also  high 
timber  to  the  south  and  southwest  15  to  20  feet  and  to  the  east  30  feet 
distant;  sharp  descent  to  orchard  below.  The  slope  in  the  orchard, 
as  a  rule,  is  quite  gradual.  The  vertical  distance  between  stations 
Nos.  1  and  3  is  570  feet,  and  the  horizontal  distance  is  3,000  feet,  a 
grade  of  12°. 


M.  W.  R.,  Supplement  No.  19. 


(To  face  p.  6.) 


Fig.  7. — Cooperative  Weather  Bureau  station,  Rock  House,  N.  C.  (near  Highlands). 


Fig.  8.— Station  No.  3,  Highlands— coldest  of  all  stations. 


M.  W  R.,  Supplement  No.  19. 


(To  face  p.  7.) 


Fig.  10. — Station  No.  1,  Blantyre,  on  State  farm  directly  below  a  northeast  slope  of  French  Broad  River. 


Fig.  11— Station  No_  2,  Blantyre,  on  State  farm  in  sag  at  base  of  Little.Fodderstack  Mountain 


Fig.  12.  Stations  Nos.  3  and  4,  Blantyre,  in  orchard  of  State  farm  on  Little  Fodderstack  Mountain, 


M.  W.  R.,  Supplement  No.  19. 


(To  face  p.  7.) 


Fig  14. — Station  No.  1,  Hendersonville. 


Fig.  15.— Station  No.  2,  Hendersonville. 


Fig.  16. — Station  No.  3,  Hendersonville. 


Fig.  18. — North  slope  in  orchard  near  Asheville,  looking  down  valley. 


Fig  -  19. — Northerly  slope  of  orchard  in  which  stations  Nos.  2  and  3  are  located 


Fig.  20.— Southerly  slope  opposite  orchard,  station  No.  2a  in  center;  station  No.  3a 
above  No.  2a  obscured  by  timber 


M.  W.  R.,  Supplement  No.  19. 


(To  face  p.  7.) 


Fig.  22.— Station  No.  1,  Tryon.  on  valley  floor  Pacelet  River,  Warrior 
Mountain  in  background 


Fig.  2.3  —Warrior  Mountain,  Tryon,  show  ing  location  of  stations  Nos. 
2,  3,  and  4. 


Fig.  28. — Station  No.  4,  Altapass;  orchard  on  steep  slope. 


Fig.  29. — Station  No.  5,  Altapass,  on  grass  plot  on  summit,  orchard  on  left  and  below 


M.  W.  R.,  Supplement  No.  19 


(To  face  p.  7.) 


Fig.  31. — Grandfather  Mountain  from  Blowing  Rock. 


Flo.  32.— Flat  Top  orchard,  Blowing  Rock,  stations  3,  t.  and  ■'>. 


Flo.  40.  Sparger  orchard.  Mount  Airy,  station  No.  1  on  extreme  left. 


Fig.  41.  -parser  orchard,  station  No.  4.  Mount  Alrv,  In  center 


THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 


ELLIJAY. 

thfir  MinCV'  °}>sen)er—^?  Elliiay  stations,  on  the  property  of 
on  a  steep  northerly  slope  of  a  spur  of  the  Cowee  Moun¬ 
tains,  the  base  station,  No.  1,  being  in  the  valley  floor  of  Ellijay  Creek 
at  an  elevation  of  2,240  feet,  while  the  high  station,  No.  5,  is  on  the 
summit  of  a  knob  1,760 'feet  above  the  base  and  4,000  feet  above  sea  level . 
k  ation  -No.  1,  in  a  field  about  30  feet  south  of  the  creek,  over  grass  plot, 
at  a  considerable  distance  from  any  trees;  across  creek  to  the  north, 


station  No.  1,  over  sod  in  apple  orchard  on  moderate  slope  though 
steeper  above  and  below,  slope  broken  up  into  ridges  and  hogbacks. 
Station  No.  4,  1,240  feet  above  station  No.  1,  in  clearing  and  on  edge 
of  steep  northerly  slope,  in  corn  and  potato  patch;  brush  about  16  feet 
to  the  west;  some  timber  100  feet  to  the  west  and  southwest.  In  winter 
sun  shut  off  during  greater  part  of  day.  Station  No.  5,  1,760  feet  above 
station  No.  1,  a  level  field  near  the  summit  of  a  high  knob,  another 
prominence,  Peak  Knob,  180  feet  higher  than  station  No.  5,  distant 
1,800  feet  to  the  south;  timber  to  the  west,  southwest  and  south,  mostly 


steep  high  slopes,  more  or  less  broken,  while  to  the  south,  slope  abrupt 
near  the  valley  floor;  orchard  at  some  distance  south  of  shelter  on  north¬ 
erly  slope  broken  and  uneven  with  natural  terraces  here  and  there; 
valley  narrow  and  trending  in  east-west  direction,  almost  entirely 
inclosed  by  mountains.  Station  No.  2,  in  orchard,  on  rather  steep 
northerly  slope  with  ferns  and  weeds  on  all  sides,  310  feet  above  station 
No.  1;  timber  to  north,  northwest,  west  and  southwest;  cleared  land 
directly  to  east,  northeast,  and  southeast,  and  for  some  distance  to  the 
south,  about  500  feet.  Station  No.  3,  the  home  station,  620  feet  above 


dead,  close  by;  abrupt  slopes  to  the  north  and  east.  (See  fig.  4,  Peak 
Knob  in  the  distance  to  the  right.)  Ellijay  Creek,  near  which  station 
No.  1  stands,  flows  in  a  westerly  direction  through  a  narrow  valley,  and 
the  slope  on  the  north  side  is  broken  up  into  spurs  and  hogbacks. 
(See  fig.  5  for  photograph  taken  from  station  No.  4,  showing  mountains 
and  slopes  on  north  side  of  Ellijay  Creek.)  For  a  vertical  distance  of 
1,760  feet  between  stations  Nos.  1  and  5  at  Ellijay,  there  is  a  hori¬ 
zontal  distance  of  about  5,100  feet,  equivalent  to  an  average  grade  of 
19°.  The  grade  on  some  portions  of  the  slope  is  more  than  30°. 


8 


SUPPLEMENT  NO.  19. 


HIGHLANDS. 

T.  G.  Earbison,  Observer. — Highlands  is  on  an  elevated  plateau 
close  to  the  Georgia  border,  and  its  group  of  five  stations  is  on  the 
property  of  the  observer  in  two  different  orchards  more  than  2  miles 
apart,  No.  1  and  2  being  in  the  Satulah  orchard  on  a  southerly  slope 
directly  below  Mount  Satulah,  and  Nos.  3,  4,  and  5  in  the  Waldheim 
orchard  on  the  southeast  slope  of  Dog  Mountain.  These  stations  have 
the  highest  elevation  of  all  used  in  the  research,  station  No.  5,  near 
the  summit  of  the  Waldheim  orchard  slope,  having  an  altitude  of 
4,075  feet.  The  place  is  near  the  southern  end  of  the  Blue  Ridge. 
There  are  several  mountain  peaks  in  the  vicinity,  the  more  prominent 
being  Satulah  and  Whiteside,  with  elevations  of  4,560  and  4,930  feet, 


feet  distant.  Timber  within  30  or  40  feet  of  shelter  and  between  it 
and  Mount  Satulah,  located  to  the  northeast  and  north,  which  towers 
directly  above  and  appears  like  an  immense  rock  reaching  an  elevation 
of  more  than  1,000  feet  above  station  No.  2.  The  grade  from  that 
station  to  the  summit  of  the  rock  is  45°,  while  the  average  grade  in  the 
orchard  itself  is  only  10°  or  11°;  timber  to  west  is  close  by  and  reaches 
also  a  little  to  the  south  and  is  rather  high.  Station  No.  3,  the  base 
station  of  the  group  in  the  Waldheim  orchard,  has  an  elevation  of 
3,675  feet  above  sea  level;  shelter  in  grass  plot  in  a  sink  immediately 
below  orchard;  slope  above  not  steep,  except  near  the  lower  edge 
directly  above  station  No.  3,  and  for  a  short  distance  above  station 
No.  4.  Station  No.  3  near  the  bottom  of  a  general  east  to  southeast 
slope,  surrounded  by  trees,  except  where  the  ground  slopes  upward 


Fig.  6. — Highlands,  contour  map  and  profile. 


respectively.  Highlands  is  only  a  few  miles  northwest  of  Rock  House 
or  Horse  Cove,  where  the  largest  amount  of  rainfall  in  the  United 
States  is  recorded  with  the  exception  of  the  extreme  north  Pacific 
coast.  (Fig.  7  shows  the  cooperative  station  at  Rock  House,  the 
thermometer  shelter  being  in  the  center  of  the  picture.)  Station 
JNo.  1,  in  the  Satulah  orchard,  the  home  station,  3,350  feet  above  sea 
level,  almost  directly  south  of  Mount  Satulah  and  about  1,500  feet 
distant  from  its  base.  The  ground  slopes  rapidly  away  from  the 
shelter  to  the  southeast  and  west.  Slope  rather  moderate  immediately 
to  the  north  in  orchard ;  in  fact,  slope  in  that  direction  does  not  become 
steep  for  more  than  1,000  feet,  but  beyond  that  point  toward  Mount 
Satulah  the  grade  is  quite  steep.  Station  No.  2,  200  feet  above  station 
No.  1,  in  a  horizontal  direction  about  1,000  feet  distant.  Shelter 
located  over  a  grassy  plot  with  apple  trees  all  around  and  only  a  few 


toward  the  orchard  on  the  northwest  side;  no  descent  on  any  side 
of  this  depression,  but  land  somewhat  broken.  The  depression  is  a 
natural  frost  pocket.  (Fig.  8  shows  station  No.  3,  looking  to  the 
northwest  toward  orchard.)  Station  No.  4,  200  feet  above  station 
No.  3,  on  a  southeast  slope  in  orchard  over  sod  covered  with  grass, 
weeds,  and  bushes  in  the  midst  of  apple  trees;  slope  at  this  point 
moderately  steep  and  in  an  east-southeast  direction.  Station  No.  5, 
400  feet  above  station  No.  3,  in  apple  orchard  20  to  30  feet  below  upper 
limit;  slope  moderate  near  shelter  and  moderately  steep  most  of  the 
way  down;  shelter  150  to  120  feet  below  the  summit  of  Dog  Mountain. 
Timber  above  orchard  to  the  west  and  northwest,  also  to  the  south, 
but  not  heavy,  the  closest  timber  being  about  25  feet  distant.  Average 
grade  between  stations  Nos.  3  and  5  is  16°,  much  greater  than  between 
stations  Nos.  1  and  2  in  the  Satulah  orchard. 


THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 


BLANTYRE. 

John  E  Davidson  Observer. -A  group  of  four  stations  on  the  State 
h  arm  at  Blantyre,  located  in  the  vallev  of  the  French  Broad  River 
which  is  rather  wide  at  this  point.  The  river  falls  here  at  the  rate 
?,  only  about  100  feet  in  35  miles  of  meandering  over  the  plateau. 
Base  station  No.  1,  close  to  the  valley  floor,  2,090  feet  above  sea  level; 
the  other  three  stations  about  a  half-mile  distant  on  the  northwest 
slope  of  Little  Fodderstack  and  separated  from  the  base  station  by  a 
gradual  ascent  partly  timbered.  Big  Fodderstack,  a  few  hundred 


southeast  and  a  small  hill  to  the  north  and  northwest;  shelter  in  lower 
edge  of  apple  orchard.  Above  station  No.  2  the  grade  rather  steep 
and  the  side  of  the  mountain  terraced;  the  slope  broken  up  consider- 
ably  in  various  directions.  The  sag  in  which  station  No.  2  is  located 
slopes  gently  from  the  southwest  to  the  northeast;  and  this  is  apart 
from  the  general  slope  thence  upward  to  summit  of  Little  Fodderstack 
in  a  southeast  to  south  direction.  Station  No.  3  in  the  midst  of  apple 
orchard,  150  feet  above  station  No.  2,  is  about  half  way  up  Little 
Fodderstack.  Shelter  located  on  a  hogback  or  ridge  50  or  60  feet 
broad  running  northwest  down  to  station  No.  2.  Slope  down,  steep, 


Fig.  9. — Blantyre,  contour  map  and  profile. 


feet  higher  than  Little  Fodderstack,  distant  about  a  mile  to  the  south¬ 
west,  but  no  high  mountains  in  the  immediate  vicinity.  Nine  or 
ten  miles  away  are  several  high  peaks,  including  Mount  Pisgah,  which 
stands  to  the  northwest  in  the  distance  with  a  maximum  height 
of  5,749  feet.  Country  in  immediate  vicinity  of  research  stations 
rolling  and  broken.  Station  No.  1,  home  station  (fig.  10),  over  a 
grass  plot  slightly  above  the  bottom  lands  on  one  of  several  terraces 
15  feet  wide,  with  moderate  slope;  gentle  slope  upward  in  rear  of 
shelter  to  the  south  and  southwest  only  few  degrees  to  base  of  Little 
Fodderstack;  to  the  southeast  of  shelter  a  peach  orchard  in  terraces 
about  30  feet  distant  from  shelter.  Station  No.  2  (fig.  11),  300  feet 
higher  than  station  No.  1,  in  a  sag  between  Little  Fodderstack  to  the 


20  feet  northwest  of  shelter,  slope  upward  directly  beyond  shelter, 
more  moderate.  Station  No.  4,  300  feet  above  station  No.  2  and  600 
feet  above  station  No.  1;  shelter  on  a  hogback  almost  on  summit  of 
Little  Fodderstack,  but  the  ground  a  few  feet  higher  to  the  south, 
southeast,  and  east;  20  to  40  feet  south  and  southeast  of  shelter  it 
slopes  almost  generally  in  all  directions.  Sparse  timber  southwest, 
south,  southeast,  and  east  of  shelter  20  to  40  feet  distant;  clear  view  at 
station  No.  4  at  sunrise  and  sunset;  shelter  located  overgrass  and  just 
beyond  upper  limit  of  orchard.  Average  grade  between  stations  Nos. 
2  and  4  about  22°,  only  a  few  slopes,  such  as  Altapass,  Ellijay,  Globe, 
and  the  China  orchard  at  Blowing  Rock  having  sections  any  steeper. 
Fig.  12  gives  good  view  of  orchard  including  stations  Nos.  3  and  4. 


10 


SUPPLEMENT  NO.  19. 


HENDERSONVILLE. 

S.  McCarson,  Observer.—  The  group  of  four  stations  at  Hendersonville 
located  3  miles  to  west  of  the  city,  the  base  station  in  a  meadow  and 
the  other  three  in  the  apple  orchard  of  Capt.  M.  0.  Toms  on  the  moderate 
slope  of  Echo  Mountain,  or  Hickory  Hill,  some  distance  southwest  of 
the  base  station.  This  group  of  stations  is  only  about  7  miles  distant 
from  Blantyre  on  the  other  side  of  the  French  Broad  River.  Jump  Off 
Mountain,  the  most  prominent  point  in  the  vicinity,  with  an  elevation 
of  3,141  feet,  lies  distant  less  than  a  mile  west  of  Echo  Mountain,  which 


respectively;  brush  and  scrub  pine  to  west  40  feet  and  timber  to  west 
about  300  feet  distant.  Station  No.  2  (fig.  15)  over  thin  grass  on  sandy 
soil  450  feet  above  station  No.  1,  and  3,500  feet  distant  in  a  horizontal 
direction  west  by  south,  at  the  bottom  of  apple  orchard;  timber,  not 
heavy,  surrounds  shelter  from  southwest  to  northeast  by  way  of  south¬ 
east,  at  varying  distances,  forming  a  semicircle.  Station  No.  3  (fig.  16) 
in  midst  of  apple  orchard,  soil  covered  with  grass,  600  feet  above 
station  No.  1,  on  a  uniform  northeast  to  east  slope  from  the  summit; 
slope  at  No.  3  more  easterly,  continuing  in  that  direction  for  descent 
of  from  40  to  50  feet,  then  a  little  gap  between  two  small  knolls  to  the 


Fig.  13.— Hendersonville,  contour  map  and  profile. 


has  an  elevation  of  2,950  feet,  there  being  a  sag  between  the  two  knobs. 
There  is  also  a  small  knob,  Mount  Davis,  a  short  distance  to  the  north 
and  of  about  the  same  elevation  as  Echo  Mountain.  Below  these 
mountains  there  is  a  more  or  less  gradual  downward  slope  in  practically 
all  directions  to  an  extensive  plain  which  reaches  for  many  miles, 
mountains  in  the  distance  surrounding.  Station  No.  1  (fig.  14),  2,200 
feet  above  sea  level  on  a  bench  some  distance  removed  from  the  valley 
floor,  on  a  grassy  plot  with  a  very  slight  declination  to  the  east;  shelter 
surrounded  by  timber  except  at  opening  to  east  through  a  narrow  gap; 
slight  slopes  upward  to  north  and  south,  on  both  of  which  timber  is 
located,  the  timber  being  30  to  50  feet  north  and  south  of  shelter, 


north  and  to  the  south.  Station  No.  4,  the  home  station,  750  feet 
above  station  No.  1,  in  apple  orchard  on  the  knoll  called  Hickory  Hill 
or  Echo  Mountain.  The  shelter  distant  10  feet  or  more  from  small 
apple  trees,  with  clover,  grass,  and  weeds  covering  the  soil.  The 
general  slope  at  Hendersonville  is  more  gradual  than  at  any  of  the 
other  places,  except  possibly  Gorge  and  Transon,  the  slope  being 
sharp  at  only  a  few  points.  The  average  grade  between  stations  Nos. 
1  and  4  is  only  7°  and  that  between  stations  Nos.  1  and  2  about  the  same. 
However,  the  grade  between  station  Nos.  3  and  4  is  somewhat  steeper. 
There  is  here  a  wider  expanse  of  surrounding  plains  than  in  the  vicinity 
of  any  other  station,  except  possibly  Wilkesboro  and  Mount  Airy. 


THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 


ASHEVILLE. 

Chas.  I .  Joyner ,  Observer. — The  five  stations  on  Mr.  Chas.  H  Webb’s 
P^Pert+y>  abo,l.lt  4  mile8  northeast,  of  the  city  of  Asheville,  on  a  bench 
bove  the  valley  of  the  French  Broad  River,  which  is  approximately 
the  center  of  the  North  Carolina  mountain  region.  Mr.  Webb’s  prop¬ 
erty  lies  on  the  north  and  south  slopes  of  Bull  Cove  Branch  (fig.  18 
photograph  taken  from  north  slope  in  the  orchard  looking  dow^i  the 


of  the  top  of  a  spur  reaching  westward  from  the  peak  of  Bull  Mountain, 
which  towers  a  thousand  feet  above,  but  station  No.  3a,  in  a  clearing 
surrounded  by  timber  on  the  opposite  slope,  is  within  about  100  feet 
of  the  summit  of  the  ridge,  projecting  across  from  Rice  Knob.  The 
southerly  slope  is  much  steeper  than  the  northerly  one.  While  stations 
Nos.  3  and  3a  are  each  380  feet  above  station  No.  1,  the  horizontal 
distance  on  the  south  slope  is  only  1,200  feet,  while  it  is  2,000  feet  on 
the  north  slope.  The  north  slope  is  broken  up  into  ridges  and  hog- 


valley  toward  the  city  of  Asheville).  Station  No.  1,  the  home  station, 
over  grass  at  an  elevation  of  2,445  feet  above  sea  level,  in  a  sag  between 
northerly  and  southerly  slopes.  Stations  Nos.  2  and  3  on  rough  broken 
soil  in  apple  orchard  (fig.  19)  on  a  northerly  slope  of  Bull  Mountain, 
155  feet  and  380  feet,  respectively,  above  station  No.  1.  Stations  Nos. 
2a  and  3a  on  the  opposite  southerly  slope  (fig.  20)  at  the  same  elevations, 
respectively,  as  stations  Nos.  2  and  3.  Station  No.  3,  only  a  few  feet 
distant  from  heavy  timber  to  the  south,  west,  and  east  within  300  feet 


backs,  but  the  south  slope  is  more  regular.  The  southerly  slope  has 
a  grade  of  nearly  18°,  while  the  opposite  northerly  slope  has  a  grade  of 
only  10.)°.  It  is  rather  level  immediately  in  the  vicinity  of  shelter  at 
No.  2  on  northerly  slope  in  the  midst  of  the  orchard,  but  quite  steep  at 
point  opposite  on  southerly  slope  where  No.  2a  is  located  in  open  field 
over  short  grass  (fig.  20).  The  shelter  at  No.  3,  because  of  its  location 
on  a  northerly  slope  and  proximity  to  timber,  is  shut  off  from  prac¬ 
tically  all  sunshine. 


30442—23 - 2 


12 


SUPPLEMENT  NO.  19. 


TRYON. 

W.  T.  Lindsey,  Observer.—1 The  stations  at  Tryon,  four  in  number, 
located  about  2  miles  to  the  northwest  of  the  village;  station  No.  1 
(fig.  22),  on  the  valley  floor  of  the  Pacolet  River,  at  an  elevation  of 
950  feet'above  sea  level,  the  lowest  of  the  experimental  stations  used 
in  this  research;  stations  Nos.  2  and  3  in  the  vineyard  of  the  observer, 
on  the  southeast  slope  of  Warrior  Mountain,  and  station  No.  4  higher 
up  on  the  slope,  with  an  elpvation  of  1,100  feet  above  station  No.  1 
and  within  400  feet  of  the  summit  (figs.  22  and  23).  There  are  several 
other  mountains  in  the  immediate  vicinity  in  the  same  range,  the 


station  No.  2  is  rather  steep  to  the  east  and  southeast,  but  almost  level 
as  station  No.  1  is  approached;  shelter  over  broken  ground  with  grass 
and  weeds,  especially  to  the  north;  timber  covers  most  of  the  slope 
between  stations  Nos.  1  and  2,  also  some  timber  to  the  east  50  to  75 
feet;  vineyard  practically  surrounded  by  timber,  terraced  and  fairly 
steep,  but  not  so  steep  as  immediately  below  or  above.  Station  No. 
3  (fig.  24),  570  feet  above  station  No.  1,  on  southeast  slope  about  50 
feet  above  upper  rim  of  vineyard;  in  a  small  apple  orchard  over  grass, 
weeds  and  rocks;  rather  a  steep  slope  above  to  station  No.  4,  with 
brush  and  high  timber  about  100  to  150  feet  to  north,  northwest,  west, 
and  southwest,  half  encircling  station.  Station  No.  4,  1,100  feet  above 


ROUND  MT, 


.WARRIOR 


BUCK  MT. 


jTjor  eh 


T  ryon 


Fig.  21. — Tryon,  contour  map  and  profile. 


most  prominent  being  Tryon  Mountain  to  the  northeast,  with  an  eleva¬ 
tion  of  3,  231  feet,  while  that  of  Warrior  is  only  2,465  feet.  Then  there 
is  Round  Mountain,  almost  midway  between  Warrior  and  Tryon. 
Across  the  Pacolet  valley  is  Melrose  Mountain  (see  fig.  24),  but  not 
near  enough  nor  of  sufficient  mass  to  serve  effectively  as  an  opposing 
slope  to  Warrior  Mountain  where  the  research  stations  were  located. 
Station  No.  1,  located  on  the  rather  wide  valley  floor  of  the  Pacolet 
River  running  in  east-west  direction,  is  well  situated  for  the  experi¬ 
mental  work,  being  at  the  foot  of  Warrior  Mountain,  on  a  grass  covered 
plot  on  ground  practically  level.  Shelter  at  the  home  station,  No.  2, 
on  lower  edge  of  vineyard,  on  southeast  slope  380  feet  above  station 
No.  1,  the  horizontal  distance  being  4,000  feet.  The  slope  below 


station  No.  1,  is  on  southeast  slope  on  edge  of  cliff  with  sharp  drop 
of  several  hundred  feet  to  station  No.  3;  is  over  grass  and  weeds  in 
small  cleared  space;  timber  and  brush  within  10  to  20  feet  on  all 
sides  except  south  and  southwest,  where  sheer  drop  occurs.  From 
station  No.  4  the  ground  slopes  upward  rather  steep  in  p laces  to  the 
summit  of  mountain  more  than  400  feet  above.  Slope  is  heavily  tim¬ 
bered  above  and  below  station  No.  4.  The  slope,  as  a  whole,  from 
station  No.  1  to  station  No.  4  has  an  average  grade  of  about  11J°>  but 
immediately  above  the  valley  floor,  between  stations  Nos.  1  and  2, 
the  grade  is  very  gentle,  while  between  stations  Nos.  2  and  4  the 
grade  is  quite  steep,  especially  above  station  No.  3.  The  average 
grade  between  stations  Nos.  2  and  4  is  about  26°. 


13 


THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 


CANE  RIVER. 

f  06s™-Cane  River  is  located  on  the  northwest 

Ll  Jk  th/oB  ai  Mountains,  and  the  orchard  stations,  four  in  number 

the  hn«^\2tml  eS  Wef  °fithie  V!Ilage’  on  the  Property  of  the  observer; 
the  base  station  in  a  level  plot  having  an  elevation  of  2,650  feet  above 

sea  level  and  somewhat  above  the  valley  floor  of  McElroy  Creek  a 
branch  of  Cane  River.  The  summit  station  is  high  up  on  a  knob 
above  a  steep  timbered  slope  1,100  feet  above  the  base  and  about 


northerly  slope;  heavy  timber  on  steep  upslope  to  the  south,  south- 
west,  and  southeast  of  shelter;  some  timber  also  to  the  east  aud  west 
more  distant;  hills  also  in  those  directions  500  or  600  feet  away;  shelter 
located  over  grass-covered  surface.  Station  No.  3,  400  feet  above 
station  No.  1,  on  northerly  slope  moderately  steep;  shelter  in  upper 
portion  of  apple  orchard  near  base  of  mountain  in  a  cove-like  inclosure, 
with  grass-covered  surface;  heavy  timber  to  east,  southeast,  south, 
southwest,  and  west.  Sun  shut  off  by  timber  during  early  morning 
and  late  afternoon  hours  for  the  greater  portion  of  the  year;  steep 


1,000  feet  distant  from  Rocky  Knob,  which  stands  250  feet  higher. 
The  country  throughout  this  section  is  rolling  and  broken  and  most 
picturesque,  with  knobs  of  various  elevations  here  and  there.  The 
two  knobs,  with  generally  sharp  profile  and  small  mass  in  proportion 
to  their  elevation,  are  isolated  peaks  which  rise  considerably  above 
surrounding  peaks  within  a  radius  of  several  miles.  Station  No.  1, 
the  home  station,  on  a  nearly  level  plot,  which  was  covered  with 
grass  in  1913  and  1914;  in  1915  and  1916  planted  in  corn;  slope  gener¬ 
ally  from  north  to  south,  but  very  slight  at  station  No.  1.  Station 
No.  2,  190  feet  above  station  No.  1,  in  apple  orchard  on  moderate 


upward  slope  to  south  and  also  where  timber  is  located  to  east;  a 
sharp  ascending  slope  covered  with  heavy  timber  from  station  No.  3 
to  station  No.  4.  Station  No.  4,  1,100  feet  above  station  No.  1,  on 
knob  with  steep  slope  downward  from  the  shelter  in  every  direction, 
except  toward  Rocky  Knob  to  south,  there  being  a  sag  between  the 
two  knobs;  small  timber  10  feet  north  and  west  of  station  No.  4,  also 
15  to  20  feet  northeast;  heavy  timber  beyond  in  practically  all  direc¬ 
tions.  The  slope,  as  a  whole,  from  station  No.  1  to  station  No.  4  has 
an  average  grade  of  16°,  being  quite  gentle  below  station  No.  3  and 
steep  above,  the  incline  above  station  No.  3  being  24°. 


14 


SUPPLEMENT  NO.  19. 


ALTAPASS. 

R.  F.  Brewer ,  Observer— Altapass  is  on  the  main  range  of  the  Blue 
Rid o^e  Mountains,  the  village  itself  being  on  the  divide  directly  north  of 
McKinney  Gap,  with  the  Black  Mountains,  including  Mount  Mitchell, 
Clingmans  Peak,  and  Celo  Mountain  standing  up  at  great  heights  to 
the  west,  Grandfather  Mountain  and  Brown  Mountain  to  the  east,  and 
smaller  knobs  in  between.  The . southeasterly  slope  containing  the 
experimental  stations  is  steep,  while  the  slope  on  the  other  side  of  the 
Blue  Ridge  to  the  north  and  northwest  is  gentle.  Five  stations  here 


timber  and  hills  to  east  and  west  200  feet  or  so.  Station  No.  3,  home 
station,  500  feet  above  station  No.  1,  shelter  in  peach  and  apple  orchard 
on  sharp  southeasterly  slope;  slope  broken  into  ridges  and  hogbacks. 
Station  No.  4  (fig.  28),  750  feet  above  station  No.  1;  shelter  in  apple 
orchard  with  small  trees  in  vicinity;  on  steep  southeasterly  slope;  soil 
badly  gullied  and  worn  away  here  by  flood  in  the  summer  of  1916. 
Station  No.  5  (fig.  29),  1,000  feet  above  station  No.  1,  on  summit  of 
ridge  200  feet  wide  and  extending  in  a  northeast-southwest  direction 
and  nearly  level  for  a  mile  or  so;  shelter  in  midst  of  small  trees  over 


are  in  the  orchard  of  the  Holston  Corporation,  the  base  station,  No.  1, 
being  2,230  feet  above  sea  level,  with  the  others  each  250  feet  above  its 
lower  neighbor.  While  the  summit  station  is  directly  on  the  main 
ridge,  No.  1  is  really  on  the  slope,  as  the  descent  below  continues  730 
feet  down  to  the  valley  floor  at  a  place  called  North  Cove,  two  miles 
distant  from  station  No.  1.  Station  No.  1  is  a  small  level  plot  in  corn¬ 
field  and  surrounded  by  dense  vegetation;  timber  and  hills  to  west, 
northwest,  and  southwest  close  by;  also  to  east  but  much  farther  away; 
hills  to  the  north.  Station  No.  2  (fig.  27),  250  feet  above  station  No.  1, 
in  small  level  plot  in  cornfield  in  midst  of  steady  southeasterly  slope; 


grass  and  weeds,  in  marked  contrast  to  the  comparatively  bare  soil  at 
the  stations  lower  down  on  the  slope,  as  shown  in  figure  28,  where  the 
vegetal  cover  is  thin  because  of  the  steepness.  The  slope  becomes 
steadily  steeper  from  station  No.  1  to  summit  and  is  especially  steep 
between  stations  Nos.  4  and  5.  The  average  grade  of  entire  slope 
from  station  No.  1  to  station  No.  5  is  about  16°  and  is  probably  more 
regular  and  uniform  than  any  other  long  slope,  except  Ellijay;  which 
has  an  average  grade  of  19°.  The  entire  Altapass  slope,  including  that 
below  station  No.  1,  is  about  1,730  feet  in  height,  and  the  Ellijay  slope 
is  1,760  feet. 


THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 

BLOWING  ROCK. 


15 


E  G.  Underdown,  Observer.— The  village  of  Blowing  Rock  is  1  neat  pH 

tL  creTL  thGprridfa  Rer/l0Untain  (fig  31)  on  the  P^ateau  f,UEh  «'ith 
tiie  crest  of  the  Blue  Ridge,  running  parallel  there  to  the  Tennessee 

boundary  line  and  distant  from  it  about  10  miles.  The  plateau  here 

" e,  a®  at  Highlands,  close  to  the  Georgia  boundary,  averages  more 

£?*’™«**  m  elevation.  To  the  west  and  south  of' the  village  there 

s  a  sharp  descent  to  the  valley  of  the  Johns  River,  and  beyond  as  far 

IpnlTn.r  T  nreit0ICring  mo,mtaills-  On  the  plateau  itself  are 
lnobsA°i  whlc.h  rnV0  °nes  lie  1°  the  north  of  the 

1  lage,  Pine  Ridge  and  Flat  Top,  with  elevations  of  4,400  feet  and  4,590 


grassy  plot,  4o0  feet  above  No.  1,  on  rather  steep  southerly  slope 
broken  up  into  ridges  and  hogbacks,  so  that  while  the  general  slope  is 
south  and  southeast  the  local  slopes  in  the  orchard  vary.  The  orchard 
extends  upward  from  station  No.  2,  with  a  rather  uniform  steepness, 
the  average  slope  in  this  orchard  is  about  15°.  The  slope  extends  320 
feet  above  ho.  2  and  1,130  feet  below  No.  1,  in  all  a  vertical  height  of 
about  1,800  feet,  even  greater  than  those  at  Altapass  and  Ellijay,  but 
for  purposes  of  the  discussion  this  slope  will  not  be  classed  with  the 
erm°ng  s*°Pes  because  of  lack  of  suitable  observation  stations.  The 
llat  Top  orchard  (figs.  32  and  33)  is  shaped  much  like  an  amphitheater 
which  gradually  slopes  down  from  the  upper  rim  to  a  lake  or  large  pond 
at  the  base.  The  basin  is  mostly  inclosed,  and  the  descent  at  the  outlet 


feet,  respectively.  The  experimental  stations  are  five  in  number, 
divided  into  two  groups,  three  in  the  Flat  Top  orchard  and  two  in  the 
China  orchard,  both  apple  orchards,  and  owned  by  Mrs.  Abram  Cohn, 
located,  respectively,  from  1  to  2  miles  north  and  northwest  of  the 
village,  and  distant  from  each  other  about  one-half  mile.  In  these  two 
and  the  Green  Park  orchard,  another  property  of  the  Cohn  family  in 
the  vicinity,  are  approximately  40,000  apple  trees,  the  three  combined 
being  probably  the  largest  property  of  the  kind  in  the  East.  The  China 
orchard,  containing  stations  Nos.  1  and  2,  is  on  a  steep  and  narrow 
southerly  slope  which  drains  into  the  Johns  River.  Station  No.  1, 
elevation  3,130  feet  above  sea  level;  shelter  over  sod  on  southerly 
slope;  timber  on  sharp  slopes  to  east,  southeast,  southwest,  and  west 
from  30  to  50  feet  from  shelter.  The  slope  continues  downward  from 
the  China  orchard  to  a  ravine  far  below.  Station  No.  2,  in  rough 


is  gradual.  The  orchard  is  broken  up  into  moderate  ridges  and  saddles, 
but  generally  all  slopes  lead  toward  the  lake,  while  beyond  hills  and 
slopes  extend  in  different  directions  with  small  gaps  between  the  hills. 
Station  No.  3  in  the  Flat  Top  orchard  has  an  elevation  of  3,580  feet, 
the  same  as  No.  2  in  the  C  hina  orchard,  and  is  on  the  valley  floor,  near  a 
large  pond  or  lake,  shown  in  figure  33,  on  an  almost  level  surface  over 
rather  thick  grass.  The  ground  at  station  No.  3  slopes  gradually  up¬ 
ward  to  the  northwest  to  a  smaller  pond,  a  steep  slope  beginning  im¬ 
mediately  beyond  and  rising  in  a  northwesterly  direction  to  stations 
Nos.  4  and  5.  There  are  sharp  slopes  on  both  sides  of  station  No.  3  to 
the  east  and  northeast  and  the  west  and  northwest,  respectively,  the 
slope  on  the  east  side  being  distant  about  25  feet,  while  that  on  the  west 
is  about  100  feet.  Station  No.  4, 175  feet  above  station  No.  3,  over  grass 
on  moderate  slope  in  midst  of  apple  trees;  the  slopes  curve  around  more 


16 


SUPPLEMENT  NO.  19. 


or  less  brokenly  tending  on  one  side  downward  toward  the  east  and  on 
the  other  toward  the  west  or  southwest.  Station  No.  5,  350  feet  above 
station  No.  3,  the  home  station;  located  on  upper  rim  of  orchard  just 
below  roadway  near  the  residence  of  owner.  Shelter  is  over  long 
grass.  From  this  station  the  orchard  stretches  down  in  all  directions, 
except  to  the  northeast,  north,  and  northwest.  The  average  slope  from 
station  No.  3  to  station  No.  5  in  the  Flat  Top  orchard  is  less  than  9°, 


compared  with  the  slope  of  15°  between  Nos.  1  and  2  in  the  China 
orchard.  There  is  a  large  extent  of  surface  area  in  the  vicinity 
of  No.  5  approximately  at  the  same  level,  and  the  surroundings  are 
much  unlike  the  knobs  on  which  several  of  the  summit  research  stations 
were  located.  No.  3  is  the  valley  floor  station  for  the  Flat  Top  group  at 
Blowing  Rock,  just  as  No.  3  at  Highlands  is  the  valley  floor  station  of 
the  Waldheim  group. 


Fig.  35. — Globe,  contour  map  and  profile. 


GLOBE. 

Julius  L.  Gragg,  Observer. — Globe,  with  its  group  of  three  stations,  is 
located  in  the  midst  of  mountains,  Grandfather  Mountain  to  the  north¬ 
west  and  Brown  Mountain  to  the  southwest.  The  Summit  station  is 
on  the  southeasterly  slope  of  a  spur  of  Grandfather,  called  Snake  Den 
Mountain.  The  valley  of  Gragg  Fork,  in  which  the  base  station  is 
located,  is  here  narrow  and  winding  and  reaches  generally  in  a  north¬ 
west-southeast  direction;  but  below,  the  direction  is  more  southerly, 
draining  the  northern  portion  of  the  eastern  slope  of  Grandfather  Moun¬ 
tain.  The  slopes  are  steep  on  both  sides  of  the  valley,  except  in  the 
lower  levels  of  the  mountain,  where  the  slope  is  gradual.  Station  No. 
1,  the  home  station,  1,625  feet  above  sea  level,  on  a  level  grass  plot 
across  Gragg  Fork  from  the  base  of  mountain,  shade  trees  in  yard  about 


25  feet  distant  from  shelter  to  the  north;  south  aud  east  is  timber  about 
300  feet  distant  and  to  the  west  about  600  feet.  Station  No.  2,  300 
feet  above  station  No.  1,  in  small  orchard  on  east  to  southeast  slope; 
shelter  in  small  patch  of  cleared  land  surrounded  by  timber  200  to  300 
feet  distant  on  side  of  mountain  on  moderate  slope,  but  steep  above  and 
below;  sunshine  cut  off  early  in  afternoon,  especially  in  late  fall  and 
winter.  Station  No.  3.  on  summit  of  ridge  1,000  feet  above  station  No. 
1  on  Snake  Den  Mountain;  shelter  in  clearing  surrounded  by  brush 
and  timber  about  20  feet  distant  in  all  directions;  grade  steep  up  the 
mountain  from  station  N o.  2  to  station  No.  3.  Timber  covers  practically 
the  entire  mountain;  peaks  all-around.  The  entire  slope  from  station 
No.  1  to  station  No.  3  averages  about  13°,  but  that  from  station  No.  2 
to  station  No.  3  averages  more  than  twice  this— 28°. 


THERMAL  BELTS  AND 


FRUIT  GROWING  IN  NORTH  CAROLINA. 


17 


gorge. 

Mountain  and^  the!  25?W*"^Gor?e  is  located  at  the  base  of  Brown 
lountain  and  the  stations,  five  in  number,  reach  along  the  Black 

^onpBdnwCh  UPi  \he-  S  0-Pe  t0  the  summit  of  Little  Chestnut  Knob,  the 
slope  downward  being  in  a  general  northeasterly  direction.  The  main 

peak  of  Brown  Mountain  is  distant  about  a  half  mile  to  the  southeast 
with  a  sag  between.  The  region  is  quite  mountainous,  but  there  are 

the  Blue  RidrJeaiieftgeh^ln  the/,mmediate  vicinity.  The  main  chain  of 
the  Blue  Ridge  lies  to  the  north,  northwest,  and  west  of  Brown  Moun¬ 
tain.  Station  No.  1  the  home  station,  1,400  feet  above  sea  level  in 
the  valley  floor  of  Wilson  Creek,  is  in  a  gap  close  to  Black  Bee  Creek 


farther  away.  Although  the  general  slope  on  this  side  of  the  mountain 
is  northeasterly,  the  ground  is  so  broken  at  No.  3  the  slope  turns  there 
to  the  southerly,  thus  forming  a  cove  or  pocket  partly  inclosed,  with 
sunshine  cut  off  m  the  afternoon.  Station  No.  4  (old),  840  feet  above 
No;  1,  in  an  abandoned  orchard  on  the  north  slope  on  a  hogback 
which  slopes  off  gently  to  the  east  and  west;  in  the  midst  of  brush, 
apple  and  other  small  trees,  and  20  to  30  feet  away  from  larger  timber 
but  none  very  large ;  station  in  operation  in  1913  and  1914  only.  Station 
No.  4  (new),  840  feet  above  No.  1,  in  operation  in  1915  and  1916,  located 
on  a  moderate  northerly  slope  in  clearing  over  thin  grass,  although  the 
general  slope  is  northeasterly.  Station  is  surrounded  by  trees  of  dif¬ 
ferent  heights  at  distances  varying  from  60  to  125  feet;  small  brush  all 


and  a  short  distance  west  of  Wilson  Creek,  into  which  Black  Bee  empties. 
The  gap  runs  from  west  to  east  between  hills  for  500  feet.  The  station, 
over  comparatively  bare  soil  and  on  rather  level  plot  with  brush  close 
at  hand,  is  surrounded  by  hills  and  mountains,  with  timber.  Sta¬ 
tion  No.  2,  in  Bagley  orchard,  290  feet  above  station  No.  1,  on  north¬ 
easterly  slope,  about  50  feet  east  of  Black  Bee  Creek.  The  valley  here 
runs  from  southwest  down  to  northeast  and  is  surrounded  by  hills,  this 
location  partaking  of  base  station  conditions.  Surface  under  shelter 
rather  bare;  slope  up  from  No.  1  to  No.  2  gentle,  as  is,  in  fact,  almost 
the  entire  slope.  Station  No.  3,  615  feet  above  No.  1  in  Chestnut 
Hollow  Cove,  on  moderate  north  to  south  slope;  timber  is  rather  thin 
and  100  to  300  feet  distant  in  all  directions.  Hills  and  mountains  are 


around.  This  station  is  distant  about  4,500  feet  in  a  horizontal  direc¬ 
tion  from  the  old  No.  4,  and  was  substituted  for  it  at  the  close  of  1914  be¬ 
cause  of  the  inconvenience  in  reaching  the  old  location.  Station  No.  5, 
1,040  feet  above  station  No.  1;  shelter  on  Chestnut  Knob  in  midst  of 
brush;  sparse  timber  distant  20  to  30  feet  in  all  directions;  knob  slopes 
off  on  all  sides,  there  being  a  level  space  of  about  30  feet  square  on  the 
top  where  shelter  stands.  The  timber  around  station  No.  5  does  not 
cast  nearly  as  much  shade  as  at  station  No.  4.  For  a  long  slope,  Gorge 
is  the  most  gradual  of  all  employed  in  this  research,  the  horizontal 
distance  between  the  base  and  the  summit  stations  being  about  2  miles 
for  a  vertical  distance  of  1,040  feet.  The  entire  slope  from  base  to 
summit  averages  only  6°. 


18 


SUPPLEMENT  NO.  19. 


TRANSON. 

Sidney  M  Transon,  Observer. — Transon  is  in  the  extreme  northern 
portion  of  the  Carolina  Blue  Ridge  region  at  a  considerable  elevation, 
the  lowest  of  the  experimental  stations  in  the  group  of  four  stations 
being  2  970  feet  above  sea  level.  The  country  m  the  immediate 
vicinity  is  rolling  and  broken  with  peaks  here  and  there  m  the  distance 


tion  No.  3,  300  feet  above  station  No.  1,  has  much  the  same  exposure  as 
No.  2,  over  grass;  rather  flat  surface  with  general  westerly  gradual  slope; 
some  timber  about  300  feet  to  the  south.  Station  No.  4,  450  feet 
above  station  No.  1,  in  a  flat  grassy  plot  on  a  small  knob.  Almost 
the  entire  slope  is  gradual,  except  immediately  below  station  No.  4. 
Stations  Nos.  1,  2,  and  3,  are  in  the  same  straight  line,  and  for  a  vertical 


although  not  so  mountainous  as  the  sections  farther  south.  The  stations 
are  on  the  property  of  the  observer.  The  base  station,  No.  1,  2,970 
feet  above  sea  level;  the  home  station,  on  a  level  grass  plot  in  a  cove 
on  the  westerly  slope  about  300  feet  above  the  valley  floor  of  Peak 
Creek;  no  timber  in  the  immediate  vicinity.  Station  No.  2,  over 
grass,  also  on  the  west  slope  150  feet  higher  up,  the  ground  being  rather 
flat  where  the  shelter  stands  and  the  general  slope  gradual.  Sta- 


difference  of  300  feet  between  stations  Nos.  1  and  3  there  is  a  horizontal 
distance  of  about  3100  feet.  While  the  general  slope  is  westerly,  it 
is  not  a  steady  decline  from  station  No.  4  to  the  base,  there  being  some 
small  secondary  hills  or  humps  on  the  way.  Above,  as  well  as  below, 
station  No.  3,  for  instance,  the  ground  descends,  and  also  at  station  No. 
2,  but  to  a  lesser  extent.  The  entire  slope  between  stations  Nos.  1  and 
4  averages  about  8°. 


THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 


WILKESBORO. 

John  Johnston,  Observer.— Wilkesboro  is  considerbly  east  of  the  Blue 
Ridge,  m  the  valley  of  the  Yadkin  to  the  north  of  the  Brushy  Mountains 
The  principal  town  there  is  now  called  North  Wilkesboro,  but  the  ex¬ 
perimental  stations,  four  in  number,  on  the  north  slope  of  the  Brushy 
Mountains,  are  nearer  to  the  old  town  of  Wilkesboro.  The  stations  are 
in  the  orchard  of  Dr.  Charles  A.  Willis  and  lie  on  a  moderate  northerly 


in  apple  orchard  across  road  just  below  station  No.  3,  on  moderate  slope 
with  grass  covered  soil.  Station  No.  3,  350  feet  above  station  No.  1, 
on  northerly  slope,  on  knob  in  orchard  over  weedy  surface;  sag  between 
it  and  station  No.  4;  ground  flat  around  shelter  for  100  to  200  feet  or  more 
then  slopes  off  all  directions.  Station  No.  4,  430  feet  above  station 
No.  1,  on  grass  covered  soil  in  apple  orchard  on  rather  level  ridge, 
extending  north  and  south  and  about  130  feet  below  summit,  of  the 


slope  at  a  point  about  midway  between  Nos.  15_  and  38,  as  shown  on  the 
relief  map.  Station  No.  1,  with  an  elevation  of  1,240  feet  above 
sea  level,  about  300  feet  above  the  valley  floor  of  the  Yadkin,  on  a 
bench  a  few  hundred  feet  in  extent  on  a  northerly  slope.  The  ground 
in  vicinity  of  station  No.  1  is  rather  uneven  and  almost  bare  of  grass  and 
about  400  feet  distant  to  the  north  descends  to  the  valley  floor  below; 
some  timber  to  the  west  of  shelter,  1,000  feet,  and  to  the  east,  120  feet. 
Station  No.  2,  on  notherly  slope,  150  feet  above  station  No.  1;  shelter 


Brushies,  which  lie  to  the  south  about  1,000  feet  or  more  across  a  sag 
running  west  to  east.  A  short  distance  to  the  north  is  a  sharp  slope 
downward;  directly  east  and  west  of  shelter  is  a  slope  downward  to 
broken  country,  and  to  the  south  200  to  300  feet  there  is  considerable 
timber.  Below  to  north,  northeast,  and  northwest  lies  a  broad  valley 
or  level  plain  extending  20  to  30  miles  to  the  Blue  Ridge  beyond. 
The  differences  in  elevation  between  these  stations  are  slight;  the  grade 
between  Nos.  1  and  3  is  13°  and  between  Nos.  1  and  4, 8°. 


20 


SUPPLEMENT  NO.  19. 


MOUNT  AIRY. 

J.  A.  Sparger,  Observer. — -Mount  Airy,  close  to  the  Virginia  border, 
is  of  course,  even  farther  than  Wilkesboro  from  the  main  mountain  re¬ 
gion,  and  in  the  viinity  there  are  only  a  few  spurs  or  peaks,  and 
these  are  of  rather  slight  elevation.  The  experimental  stations  here, 
four  in  number,  are  on  the  property  of  the  Sparger  Orchard  Co.,  about 
6  miles  east  of  the  city  of  Mount  Airy,  on  Slate  Mountain,  station 
No.  1  at  the  base,  stations  Nos.  2  and  3  on  the  western  and  eastern  slopes, 


directions  is  rather  flat,  but  the  land  becomes  rolling  as  the  mountain 
is  approached.  Station  No.  2,  in  orchard  in  cultivated  area,  160 
feet  above  station  No.  1,  on  fairly  steep  westerly  slope,  with  timber 
150  feet  upslope;  the  land  on  this  slope  somewhat  broken  to  the  north 
and  south;  slope  to  the  south  rather  moderate,  but  steep  to  north  from 
a  point  30  feet  from  shelter.  Station  No.  3,  on  easterly  slope,  with 
the  same  elevation  as  station  No.  2;  slope  more  gradual  as  compared 
with  the  westerly  slope;  not  in  orchard  but  on  rough  weedy  ground, 
and  between  it  and  the  summit  is  a  belt  of  timber.  Station  No.  4 


respectively,  and  station  No.  4  at  the  summit.  Slate  Mountain 
overlooks  the  city  of  Mount  Airy,  which  stands  on  a  broad  plain  to  the 
west.  Distant  10  to  20  miles  farther  west  are  the  Sorrytown  Mountains, 
a  branch  of  the  Blue  Ridge,  extending  in  a  southwesterly  direction 
and  across  the  Yadkin  to  the  southwest,  30  miles  or  more  away  are  the 
Brushy  Mountains.  To  the  east  is  a  broken  country  for  15  to  30  miles 
with  several  spurs  of  varying  heights.  Station  No.  1  (fig.  40),  the 
home  station,  1,340  feet  above  sea  level,  on  a  level  plot  of  grass,  some¬ 
what  distant  from  the  base  of  the  mountain  on  which  the  orchard  is 
located.  The  country  near  station  No.  1  for  several  hundred  feet  in  all 


(fig.  41),  in  orchard  360  feet  above  station  No.  1,  is  on  the  summit  of 
the  ridge  200  feet  across  and  almost  level,  with  slight  slopes  leading 
thence  directly  toward  the  west  and  east.  The  ridge  runs  from  north¬ 
east  to  southwest  1  mile,  undulating  somewhat  brokenly;  a  portion  of 
the  ridge  to  the  northeast  about  a  quarter  of  a  mile  away  is  about  30 
feet  higher  than  shelter  No.  4.  Horizontal  distance  between  station 
No.  3  and  the  summit  is  nearly  three  times  as  great  as  the  distance 
between  the  summit  and  station  No.  2.  The  average  grade  on  the 
westerly  slope  between  stations  Nos.  2  and  4  is  16°,  as  compared  with  the 
average  grade  on  the  easterly  slope  between  stations  Nos.  3  and  4  of  10°. 


THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 


21 


ARRANGEMENT  OF  TABLES. 

It  is  necessary  to  limit  the  publication  of  the  tabular 
matter  to  the  smallest  size  consistent  with  an  under¬ 
standing  of  the  problems  under  consideration.  If  only 
a  few  slopes  were  under  investigation,  it  might  have 
been  possible  to  publish  the  data  in  greater  detail,  as 
there  would  then  have  been  a  relatively  small  number  of 
stations  involved;  but  in  this  case  we  shall  have  to  be 
content  for  the  most  part  with  summarized  tables,  except 
when  it  becomes  necessary  in  expounding  certain  theories 
to  give  daily  and  hourly  values. 

The  average  maximum,  average  minimum,  absolute 
maximum,  and  absolute  minimum  temperature,  and  the 
absolute  and  average  range  and  mean  temperature  will 
be  discussed  in  the  order  named,  and  then  will  follow 
special  chapters  on  inversion  and  norm  conditions, 
frosts,  lengths  of  the  growing  season,  and  a  few  supple¬ 
mentary  studies  bearing  upon  the  situation.  Graphs 
have  been  employed  to  emphasize  special  features,  and 
it  is  thought  that  those,  together  with  the  tables,  will 
be  considered  sufficiently  comprehensive. 

Physical  explanation  of  local  variation  in  temperature. — 
Before  taking  up  the  discussion  of  the  observational 
data  or  dealing  with  the  question  of  temperature  and 
circulation  within  the  valleys,  it  appears  highly  important 
to  present  in  a  connected  form  a  somewhat  comprehensive 
explanation  of  the  causes  of  the  conditions  which  the 
observations  disclose. 

It  must  be  recognized  that  the  progressive  changes 
of  temperature  from  hour  to  hour  and  from  day  to  day  at 


any  one  locality  result  from  a  great  many  causes,  but  our 
present  problem  is  chiefly  concerned  with  changes  going 
on  between  daytime  and  nighttime  in  mountain  valleys 
at  times  when  the  atmosphere  is  clear  and  little  or  nor 
wind  prevails,  especially  at  night.  Even  in  the  daytime 
on  these  occasions  the  motions  of  the  atmosphere  are 
more  or  less  dominated  by  local  influences  rather  than  the 
general  cyclonic  or  anticyclonic  circulation  and  changes 
of  temperature  are  then  due  primarily  to  solar  insolation 
in  the  daytime  and  radiation  at  night. 

It  is  well  known  that  atmospheric  absorption  and 
radiation,  especially  when  the  atmosphere  is  relatively 
dry  or  free  from  clouds,  are  very  small.  Important 
changes  of  temperature  are  then  brought  about  chiefly 
by  contact  with  the  earth’s  surface,  which  is  warm  or  cold 
according  to  circumstances.  It  is  important  to  recognize 
that  on  this  account  we  must  regard  the  walls  and  floors 
of  valleys  as  the  primary  heating  agency  of  the  atmosphere 
during  the  daylight  hours,  and,  conversely,  during  the 
nighttime  these  same  walls  and  floors  are  the  primary 
cooling  agencies  by  reason  of  the  active  loss  of  tempera¬ 
ture  by  the  surface  cover  and  vegation  of  the  walls,  due 
to  nocturnal  radiation. 

The  processes  by  which  the  heating  in  the  daytime 
and  the  cooling  which  occurs  at  nighttime  communicate 
heat  to  the  atmosphere  or  receive  heat  from  the  atmos¬ 
phere  are  the  phenomena  which  we  will  try  to  make  clear 
in  the  interpretation  of  such  observational  data  as  have 
been  collected  in  this  study. 


■ 

. 


. 


: 


23 


THERMAL  BELTS  ANB  FRUIT  GROWING  IN  NBRTH  CAROLINA. 

TEMPERATURE. 


MAXIMUM  TEMPERATURE. 

In  the  discussion  of  average  maximum  temperature 
Table  1  is  supplemented  by  Tables  la,  lb,  lc,  and  Id. 

The  avearge  maximum  readings  contained  in  these 
tables  are  deduced  from  the  maxima  observed  during  the 
daytime  only,  instead  of  the  24-hour  maxima,  just  as 
later  in  the  discussion  of  the  mean  minimum  temperature 
night  minima  only  are  used.  This  plan  has  been  adopted 
in  order  to  make  possible  comparisons  of  day  conditions, 
on  the  one  hand,  and  of  night  conditions,  on  the  other, 


and  the  influence  of  maxima  that  occurred  in  the 
nighttime  or  minima  in  the  daytime  will  thus  be 
eliminated. 

The  maxima  in  the  mountain  region  vary  considerably 
because  of  difference  in  latitude,  elevation  above  sea 
level,  character  of  the  weather,  whether  cloudy  or  sun¬ 
shiny,  shade  from  neighboring  timber,  hills,  or  mountains, 
the  direction  and  degree  of  inclination  of  the  slope,  the 
seasonal  variation  of  the  sun,  the  character  and  amount 
of  vegetal  cover,  and  the  absolute  and  relative  humidity 
of  the  air. 


Table  1. —  Monthly  and  annual  average  maximum  temperatures,  1913-1916. 

[The  differences  between  the  averages  at  the  base  station  and  those  of  the  respective  slopes  may  be  seen  by  simple  inspection.) 


Principal  and  slope  stations 
elevation  above  mean  sea  level 
of  base  station  (feet). 

Height  of 
slope  sta¬ 
tion  above 
base 
(feet). 

Janu¬ 

ary. 

Febru¬ 

ary. 

March. 

April. 

May. 

June. 

Altapass: 

No.  1,  base  station,  eleva¬ 
tion  2,  230 . 

'47.4 

1 47.3 

150.7 

65.7 

75.0 

79.3 

No.  2,  SE . 

250 

1  46.6 

146.4 

1  49.6 

64.8 

74.6 

79.0 

No.  3,  SE . 

500 

144.9 

1  44.7 

1  48. 0 

63.3 

73.2 

77.4 

No.  4,  SE . 

750 

1  43.9 

1  43.4 

1  47.4 

62.0 

71.8 

76.1 

No.  5,  summit . 

1,000 

1  43. 1 

142.7 

1  46.6 

61.5 

70.8 

75.3 

Asheville: 

No.  1,  base  station,  eleva¬ 
tion  2,445 . 

50.8 

48.2 

52.2 

64.8 

75.2 

79.5 

No.  2,  N . 

155 

49.4 

46.7 

51.2 

64.0 

74.8 

78.8 

No.  2a,  S . 

155 

50.1 

47.7 

51.5 

63.9 

74.0 

78.2 

No.  3,  N . . 

380 

47.0 

44.9 

49.6 

63.0 

72.8 

75.9 

No.  3a,  S . 

380 

51.0 

48.8 

52.9 

66.3 

75.6 

79.2 

Blantyre: 

No.  1,  base  station,  eleva¬ 
tion  2,090 . 

52.5 

51.2 

55.8 

68.2 

78.0 

82.0 

No.  2,  NW . 

300 

50.8 

49.3 

54.3 

67.7 

77.8 

81.4 

No.  3;  NW . 

450 

50.7 

49.2 

52.4 

67.1 

77.3 

80.  S 

No.  4,  NW . 

eoo 

51.3 

51.0 

54.6 

68.9 

77.9 

81.6 

Blowing  Rock: 

No.  1,  base  station,  eleva- 

44.5 

42.5 

46.4 

59.0 

69.8 

74.4 

No.  2,  S . 

450 

44.0 

42.5 

46.1 

59.0 

69.2 

74.2 

No.  3,  SE . 

450 

42.8 

41.2 

44.7 

58.2 

68. 2 

73.2 

No.  4,  SE . 

625 

43.5 

41.8 

45.1 

57.8 

68.2 

73.4 

No.  5,  SE . 

800 

43.0 

40.6 

44.8 

57.8 

67.7 

73.0 

Bryson: 

No.  1,  base  station,  eleva- 

2  52. 2 

151.3 

154.1 

69.0 

79.2 

83.5 

No.  2,  h . 

385 

2  50. 6 

151.1 

1  54.1 

68.9 

79.4 

82.8 

No.  2a,  S . 

385 

2  52. 3 

152.2 

155.1 

69.8 

79.7 

82.9 

No.  3,  summit . 

570 

2  51.1 

152.1 

155.9 

72.7 

81.6 

84.1 

Cane  River: 

No.  1,  base  station,  eleva- 

1  47.9 

146.0. 

148.5 

63.6 

74.1 

78.5 

No.  2,  N . 

190 

1  46.9 

1  45. 5 

14S.  2 

63.3 

73.9 

78.4 

No.  3,  NE . 

400 

143.2 

1  42.6 

1  46.7 

62.8 

73.5 

77.4 

77.2 

1,100 

144.1 

1  42.9 

1  46.1 

62.6 

74.6 

Ellijay: 

No.  1,  base  station,  eleva- 

151.4 

151.0 

153.6 

68.1 

78.1 

81.8 

No.  2,  N . 

310 

1  50.2 

1  50.2 

1  52.9 

67.1 

77.1 

80.  8 
79.0 
76.8 

1  75.3 

No.  3^  N . 

620 

149.1 

148.6 

151.3 

64.9 

75.0 

No.  4,'  N . 

1,240 

1  45. 0 

145.1 

148.4 

63.5 

73.6 

1,760 

2  45. 8 

2  46.0 

1  48.2 

1  63.0 

172.7 

Globe: 

No.  1,  base  station,  eleva- 

50.5 

50.0 

54.8 

67.9 

78.2 

82.2 

No.  2,  E . 

300 

48.2 

49.0 

54.0 

67.8 

77.4 

80. 1 
80.1 

1,000 

48.0 

48.  2 

53.1 

67.3 

77.4 

Gorge: 

No.  1,  base  station,  eleva- 

50.0 

50.5 

56.3 

69.7 

80.3 

83.9 

82.0 

79.8 

80.8 
80.1 

No.  2  'l^E . 

290 

50.2 

49.6 

54.8 

68.0 

78.5 

No.  3*  S . 

615 

49.1 

48.2 

53.6 

66. 4 

76.4 

No.  i)  N.  (old);  NE.  (new).. 

840 
1, 040 

48.5 

48.0 

4S.0 

47.9 

53.3 

53.1 

67.1 

67.0 

77.4 

76.8 

Hendersonville: 

No.  1,  base  station,  eleva- 

>48.9 

149.8 

153.4 

67.2 

76.7 

80.6 

78.5 

77.5 
77.2 

450 

147.0 

147.0 

1  50. 

64.6 

74. 6 

Nn  3'  E  . 

600 

1  47. 1 

146.6 

1  49.7 

63.8 

73.7 

750 

1  46.0 

145.9 

1  49.0 

63.3 

73.4 

Highlands: 

No.  1,  base  station,  eleva¬ 
tion,  33150 . 

No  2  SE . 

. 266" 

145.9 

147.3 

144.1 

147.4 

148.6 

147.9 

62.8 

62.6 

72.4 
73.0 
73.0 

70.5 
70.8 

75.9 

76.2 

73.8 

73.9 
74.4 

No.  3^  SE . 

325 

M3. 1 

142.9 

146.1 

60.7 

60.1 

No.  A,  SE . 

525 

143. 1 

1  42.0 

1  44.2 

No.  5,  SE . 

725 

142.7 

141.9 

1  43. 6 

60. 4 

Mount  Airy: 

No.  1,  base  station,  eleva- 

49.7 

48.7 

54.6 

68.4 

78.5 

78.1 
77.4 

77.2 

84.6 

Nn  2  W  . 

160 

48.4 

147.2 

53.6 

67.2 

66.8 

1  66.9 

No  3  E . 

160 

48.8 

47.4 

!  53.7 

82.1 

360 

47.6 

47.0 

1  53. 5 

1 3-year  average. 

July. 

I 

August. 

Septem¬ 

ber. 

October. 

Novem¬ 

ber. 

Decem¬ 

ber. 

Annual. 

82.0 

81.2 

74.9 

68.2 

58.6 

46.8 

64.  S 

81.1 

80.2 

74.8 

67.9 

57.6 

46.2 

64. 1 

79.2 

78.4 

72.7 

65.4 

55.8 

44.6 

62.3 

78.1 

77.6 

71.3 

64.7 

55.2 

43.1 

61.2 

77.7 

76.9 

71.2 

63.8 

54.6 

43.0 

60.6 

81.9 

81.5 

76.2 

68.2 

59.0 

47.6 

65.4 

81.1 

‘80.2 

174.8 

66.1 

56.9 

46.0 

64.2 

80.4 

80.2 

75.3 

67.2 

58.2 

47.3 

64.5 

78.0 

76.8 

70.4 

62.4 

53.8 

43.6 

61.5 

81.2 

80.3 

74.8 

67.  S 

60.6 

48.3 

65.6 

83.8 

82.5 

76.4 

68.7 

60.2 

48.2 

67.3 

82.9 

81.5 

75.4 

68.2 

59.5 

47.4 

66.4 

82.4 

81.1 

74.8 

68.3 

59.7 

47.4 

66.1 

83.0 

82.3 

76.7 

69.5 

60.8 

4S.0 

67.2 

76.8 

75.6 

69.9 

62.4 

52.9 

42.0 

59.7 

76.1 

74.4 

69.3 

61.8 

53.0 

42.3 

59.4 

75.1 

73.8 

68.0 

61.2 

51.8 

41.3 

58.3 

75.8 

74.6 

68.9 

61.4 

52.5 

42.2 

58.8 

75.4 

74.2 

68.3 

60.8 

51.6 

41.3 

58.2 

85.6 

84.9 

79.8 

71.4 

1  61.4 

1  48.3 

68.4 

84.8 

84.2 

79.2 

70.4 

*  59.8 

‘46.4 

67.6 

84.7 

83.8 

79.0 

71.4 

161.6 

*  48.2 

68.4 

84.9 

84.0 

78.6 

70.1 

1  60.2 

1  46.3 

68.5 

81.3 

80.7 

75.1 

66.9 

57.2 

45.7 

63.8 

80.6 

79.7 

73.8 

66.0 

56.9 

45.1 

63.2 

79.2 

77.6 

70.8 

61.9 

52.0 

41.4 

60.8 

79.0 

77.4 

70.7 

62.8 

54.4 

42.9 

61.2 

83.8 

83.1 

78.2 

70.3 

61.3 

49.8 

67.5 

82.9 

81.8 

77.2 

68.9 

60.0 

48.6 

66.5 

81.0 

80.0 

74.6 

67.4 

58.6 

47.7 

64.8 

79.0 

78.2 

72.5 

64.6 

155.1 

44.1 

62.2 

177.0 

‘76.8 

1  72.1 

1  64.4 

155.0 

1  44.1 

‘61.7 

84.5 

82.8 

77.1 

70.4 

60.8 

48.4 

67.4 

1  82.1 

1  81.3 

75.3 

68.1 

58. 1 

45.5 

65.6 

82.1 

80.4 

74.2 

67.3 

58.4 

45.8 

65.2 

86.3 

84.0 

77.8 

70.9 

60.8 

47.4 

68.2 

84.5 

83.4 

77.4 

69.6 

60.0 

47.2 

67.1 

82.4 

81.0 

75.2 

68.4 

59.4 

46.7 

65. 6 

82.7 

81.4 

74.6 

67.6 

57.9 

45.9 

65.4 

82.2 

80.4 

73.7 

66.4 

58.4 

45.4 

65.0 

83.0 

81.2 

75.0 

68.0 

59.1 

47.2 

65.8 

80.7 

79.2 

73.3 

65.9 

57.1 

45.9 

63.7 

80.2 

78.5 

72.4 

64.8 

56.5 

45.0 

63.0 

79.8 

78.6 

72.6 

65.0 

56.2 

44.6 

62.6 

77.6 

76.8 

71.6 

64.4 

56.6 

45.8 

61.9 

77.4 

77. 1 

71.8 

64.6 

56.2 

40.  6 

62. 5 

75.4 

75.1 

69.2 

62.4 

54.4 

43.9 

60.0 

75.8 

76.2 

68.6 

61.5 

53.8 

42.8 

59.4 

76.5 

75.4 

69.2 

‘62.2 

54.6 

43.5 

5y.  6 

85.8 

85.2 

83.0 

82.4 

77.7 

77.1 

69.5 

68.8 

59.2 

58.2 

46.7 

45.5 

67.2 

66.3 

84.8 

84.2 

82.3 

81.7 

77.0 

75.9 

68.4 

67.9 

58.2 

57.8 

46.2 

45.4 

66. 1 
65.6 

2  2-year  average. 


24 


SUPPLEMENT  NO.  19. 

Table  1. — Monthly  and  annual  average  maximum  temperatures,  1918-1916 — Continued. 

[The  differences  between  the  averages  at  the  base  station  and  those  of  the  respective  slopes  may  be  seen  by  simple  inspection.] 


Principal  and  slope  stations 
elevation  above  mean  sea  level 
of  base  station  (feet). 

Height  of 
slope  sta¬ 
tion  above 
base 
(feet). 

Janu¬ 

ary. 

Febru¬ 

ary. 

March. 

April. 

May. 

June. 

July. 

August. 

Septem¬ 

ber. 

October. 

Novem¬ 

ber. 

Decem¬ 

ber. 

Annual. 

Transon: 

No.  1,  base  station,  eleva- 

46.2 

43.8 

48.4 

61.8 

71.9 

77.1 

79.6 

78.1 

72.7 

65.2 

54.6 

43.8 

61.9 

No.  2,  W . 

150 

44.1 

48.0 

46.3 

60.2 

69.8 

75.2 

77.0 

75.8 

69.3 

61.6 

52.4 

41.2 

59.8 

No.  3,  W . 

300 

44. 1 

42.0 

46.4 

60.7 

70.2 

75.7 

77.8 

76.1 

70.7 

62.9 

52.7 

41.2 

60.0 

No.  4,  Summit . 

450 

1  41.4 

141.1 

i  43.5 

58.4 

68.1 

73.9 

76.1 

75.1 

69.8 

60.7 

51.3 

40.3 

58.4 

Tryon: 

No.  1,  base  station,  eleva- 

54.6 

54.3 

59.2 

71.7 

81.4 

86.2 

88.6 

86.7 

80.9 

74.0 

63.8 

51.8 

71.1 

No.  2,  SE . 

380 

53.4 

53.9 

59.0 

72.0 

81.4 

83.4 

88.1 

86.2 

80.6 

73.2 

63.9 

51.5 

70.6 

No.  3,  SE . 

570 

52.0 

51.9 

56.3 

69,2 

78.8 

80.7 

85.1 

83.8 

77.6 

68.9 

60.7 

48.7 

68.0 

No.  4,  SE . 

1,100 

51.6 

.50.7 

55.4 

68.0 

77.1 

79.0 

84.2 

82.9 

77.0 

70.4 

61.1 

48.5 

67.3 

Wilkesboro: 

No.  1,  base  station,  eleva¬ 
tion,  1,240 . 

51.4 

50.4 

56.3 

69.8 

79.4 

85.2 

87.5 

84.9 

79.2 

71.8 

61.1 

48.6 

68.8 

No.  2,  N . 

150 

50.6 

49.8 

55.8 

69.5 

79.7 

84.6 

87.2 

84.3 

77.6 

70.0 

60.0 

46.9 

68.0 

No.  3,  N . 

350 

50.6 

49.3 

55.4 

68.1 

78.0 

82.7 

84.9 

82.7 

76.0 

69.0 

59.4 

47. 1 

66.9 

No.  4,  W . 

430 

50.0 

48.6 

54.6 

68.0 

76.8 

82.1 

84.5 

82.6 

75.7 

68.0 

59.2 

46.7 

66.4 

1 3-year  average. 


3  2-year  average. 


Table  ia. — • Average  maximum  temperatures  during  selected  clear 

periods. 

[The  differences  between  the  averages  at  the  base  station  and  those  of  the  respective 
slope  stations  may  be  seen  by  simple  inspection.) 


Principal  and  slope  stations;  elevation  above  mean 
sea  level  of  base  station  (feet). 

Height  of 
slope 
station 
above 
base 
(feet). 

Clear 

period— 

May 

19-26,  in¬ 
clusive, 
1914. 

Clear 
period — 
Nov.  1-7 
and  22-26, 
inclusive. 
1914. 

Altapass: 

SO.  6 

64.3 

No.  2,  SE . 

250 

80.1 

63.7 

No.  3,  SE . 

500 

78.8 

61.3 

No.  4,  SE . 

750 

77.9 

60.9 

No.  5,  summit . 

1,000 

76.1 

59.8 

Asheville; 

81.0 

62.2 

60.0 

No.  2,  N . 

155 

80.4 

No.  2a,  S . 

155 

78.4 

62.8 

No.  3,  N . 

380 

77.5 

56.2 

No.  3a,  S . 

380 

80.6 

67.6 

Blantyre; 

No.  1,  base  station,  elevation  2,090 . 

83.0 

66.4 

65.6 

No.  2,  NW . 

300 

84.1 

No.  3,  NW . 

450 

83.5 

65. 5 

No.  4,  NW . 

600 

84.6 

66.5 

Blowing  Rock; 

No.  1,  base  station,  elevation  3,130 . 

75.8 

58.0 

58.1 

No.  2,  S . 

450 

74.0 

No.  3,  SE., . 

450 

73.1 

55.8 

No.  4,  SE . 

625 

73.5 

58.2 

No.  5,  SE . 

800 

72.8 

55.9 

Bryson: 

No.  1,  base  station,  elevation  1,800 . 

84.7 

67.4 

65.5 

No.  2,  N . 

385 

84.9 

No.  2a,  S . 

385 

84.5 

67.8 

No.  3,  summit . 

570 

86.0 

65.5 

Cane  River: 

No.  1,  base  station,  elevation  2,650 . 

79.8 

61.2 

60.8 

No.  2,  N . 

190 

78.8 

No.  3,  NE . 

400 

78.6 

56.0 

No.  4,  summit . 

1,100 

81.8 

58.3 

Ellijay: 

No.  1,  base  station,  elevation  2,240 . 

80.9 

66.2 

No.  2,  N . 

310 

82.1 

63.8 

No.  3,  N . 

620 

79.1 

63.6 

No.  4,  N . 

1,240 

78.8 

58.8 

No.  5,  summit . 

1,760 

77.5 

60.3 

Table  la. — Average  maximum  temperatures  during  selected  clear 
periods — Continued. 

[The  differences  between  the  averages  at  the  base  station  and  those  of  the  respective 
slope  stations  may  be  seen  by  simple  inspection.] 


Principal  and  slope  stations:  elevation  above  mean 
sea  level  of  base  station  (feet). 

Height  of 
slope 
station 
above 
base 
(feet). 

Clear 
period — 
May 

19-26,  in¬ 
clusive, 
1914. 

Clear 
period — 
Nov.  1-7 
and  22-26, 
inclusive, 
1914. 

Globe: 

No.  1.  base  station,  elevation  1,625 . 

84.0 

67.  2 

No.  2,  E . . . . 

300 

83.8 

62.0 

No.  3,  summit . 

1,000 

83.9 

65.3 

Gorge: 

No.  1,  base  station,  elevation  1,400 . 

87. 1 

67.8 

66.2 

No.  2,  NE . 

290 

85.2 

No.  3,  S . 

615 

82.9 

66.0 

No.  4,  NE . 

840 

83.2 

67.1 

No.  5,  summit . 

1,040 

82.6 

65.5 

Hendersonville: 

No.  1,  base  station,  elevation  2,200 . 

82.6 

65.  2 

No.  2,  E . 

450 

81.0 

61.9 

No.  3,  E . 

600 

79.6 

62.0 

No.  4,  summit . 

750 

79.0 

61.5 

Highlands: 

No.  1,  base  station,  elevation  3,350 . 

76.2 

60. 1 

No.  2,  SE . 

200 

78.2 

64.1 

No.  3,  SE., . 

325 

74.6 

58.8 

No.  4,  SE . 

525 

74.2 

57.7 

No.  5,  SE . 

725 

75.9 

60.8 

Mount  Airy: 

No.  1,  base  station,  elevation  1,340 . 

85. 1 

65.0 

62.7 

No.  2,  W . 

160 

85.1 

No.  3,  E . 

160 

83.2 

63.1 

No.  4,  summit . 

360 

83.6 

62.8 

Transon: 

No.  1,  base  station,  elevation  2,970 . 

77.6 

58.3 

55.6 

No.  2,  W . 

150 

75.6 

No.  3,  W . 

300 

77.2 

55.8 

No.  4,  summit . 

450 

74.4 

55.3 

Tryon: 

No.  1,  base  station,  elevation  950 . 

87.5 

89.0 

72.0 

71.6 

No.  2,  SE . 

380 

No.  3,  SE . 

570 

83.4 

69.2 

No.  4,  SE . 

1,100 

81.5 

68.3 

Wilkesboro: 

No.  1,  base  station,  elevation  1,240 . 

87. 1 

67.5 

66.2 

No.  2,  N . 

150 

85.8 

No.  3,  N . 

350 

83.9 

65.7 

No.  4,  W . 

430 

83.2 

64.8 

25 


THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 


Table  lb.  Average  differences  between  the  maximum  temperatures  at  the  base  station  and  those  higher  up  on  the  three  long  slopes  of  Altapass,  Ellijay, 

and  Gorge  on  selected  days  of  cloudy  weather  in  1915. 


ALTAPASS. 

Feet. 

Difference. 

No.  1,  base  station . 

No.  2,  SE.  slope . 

250 

-0.7 

No.  3,  SE.  slope . 

500 

—1.5 

No.  4,  SE.  slope . 

750 

-2.1 

No.  5,  summit . 

Average,  1°  for  each  312  feet. 

1,000 

-3.2 

ELLIJAY. 

Feet. 

Difference. 

GORGE. 

Feet. 

Difference. 

No.  1,  base  station . 

No.  2,  N.  slope . 

No.  3,  N.  slope . 

No.  4,  N.  slope . 

No.  5,  summit . 

Average,  1°  for  each  326  feet. 

310 

620 

1,240 

1,760 

-0.7 

-2.1 

-3.7 

-5.4 

No.  2,  NE.  slope . 

No.  3,  S.  slope . 

No.  4,  W.  slope . 

No.  6,  summit . 

Average,  1°  for  each  347  feet. 

290 

615 

840 

1,040 

-0.7 

-1.8 

-2.4 

-3.0 

Table  lc. — Monthly  and  annual  average  maximum  temperatures  on  six  long  slopes  and  rate  of  decrease  with  elevation,  1913-1916. 

[The  slopes  selected  for  this  comparison  have  a  difference  in  elevation  1,000  feet  or  more  between  base  and  summit  stations.  The  differences  in  temperature  between  the  base  and 

summit  stations  are  given,  as  well  as  the  difference  in  feet,  for  each  degree  difference  in  temperature.] 


Slopes  and  stations. 

Elevation  (feet).1 

Month. 

Base. 

Summit. 

Janu¬ 

ary. 

Febru¬ 

ary. 

March. 

April. 

May. 

June. 

July. 

Au¬ 

gust. 

Septem¬ 

ber. 

Octo¬ 

ber. 

Novem¬ 

ber. 

Decem¬ 

ber. 

An¬ 

nual. 

Altapass,  No.  1 . 

2,230 

2  47.4 

2  47. 3 

2  50.7 

2  65. 7 

75.0 

79.3 

82.0 

81.2 

74.9 

68.2 

58.6 

46.8 

64.8 

Altapass^  No.  5 . 

1,000 

2  43. 1 

2  42. 7 

2  46.6 

2  61.5 

70.8 

75.3 

77.7 

76.9 

71.2 

63.8 

54.6 

43.0 

60.6 

Difference . 

—4.3 

-4.6 

—4. 1 

—4.2 

-4.2 

-4.0 

-4.3 

-4.3 

-3.7 

-4.  4 

-4.0 

-3.8 

-4.2 

Feet  for  1“  difference . 

233 

217 

244 

238 

238 

250 

233 

233 

270 

227 

250 

263 

238 

Cane  River,  No.  1 . 

2,650 

2  47.9 

2  46.0 

2  48.5 

63.6 

74.1 

78.5 

81.3 

80.7 

75.1 

66.9 

57.2 

45.7 

63.8 

Cane  Riveri  No.4 . 

1,100 

2  44. 1 

2  42.9 

2  46. 1 

62.6 

77.2 

79.0 

77.4 

70.7 

62.8 

54.4 

42.9 

61.2 

Difference . 

—3.8 

—3.1 

—2.4 

-1.0 

+0.5 

-1.3 

-2.3 

-3.3 

-4.4 

-4. 1 

-2.8 

-2.8 

-2.6 

Feet  for  1°  difference  4 . 

289 

355 

458 

1,100 

2,200 

846 

478 

333 

250 

268 

393 

393 

423 

Ellijay,  No.  1 . 

2, 240 

*  51. 4 

>51.0 

>53.6 

68.1 

78.1 

81.8 

83.8 

83.1 

78.2 

70.3 

61.3 

49.8 

67.5 

Ellijay’  No.  5 . 

1,760 

s  45.8 

»  46.0 

>48.2 

>63.0 

>  72.7 

>  75. 3 

>  77. 0 

>76.8 

>72.1 

>  64.4 

>  55.0 

>44.1 

61.7 

-5.6 

-5.0 

-5.4 

-5.1 

-5.4 

-6.5 

-6.8 

-6.3 

-6.1 

-5.9 

-6.3 

-5.7 

-5.8 

Feet  for  1 0  difference . 

314 

352 

326 

345 

326 

271 

259 

279 

2S9 

298 

279 

309 

303 

Globe,  No.  1 . 

1,625 

50.5 

50.0 

54.8 

67.9 

78.2 

82.2 

84.5 

82.8 

77.1 

70.4 

60.8 

48.4 

67.4 

Globe,  No.  3 . 

1,000 

48.0 

48.2 

53.1 

67.3 

77.4 

80.1 

82.1 

80.4 

74.2 

67.3 

58.  4 

45.  8 

65.2 

-2.5 

—1.8 

—1.7 

-0.6 

-0.8 

-2.1 

-2.4 

-2.4 

-2.9 

-3. 1 

-2.4 

-2.6 

-2.2 

400 

556 

588 

1,667 

1,250 

476 

417 

417 

345 

323 

417 

385 

455 

1,400 

50.0 

50.5 

56.3 

69.7 

SO.  3 

83.9 

86.3 

84.0 

77.8 

70.9 

60.8 

47.4 

68.2 

1,040 

48.0 

47.9 

53.1 

67.0 

76.8 

80.1 

82.2 

80.4 

73.7 

66.  4 

58.4 

45.4 

65.0 

-2.0 

-2.6 

-3.2 

-2.7 

-3.5 

-3.8 

-4.1 

-3.6 

-4.1 

-4.5 

-2.4 

-2.0 

-3.2 

520 

400 

325 

385 

297 

274 

254 

289 

254 

231 

433 

520 

325 

950 

54.6 

54.3 

59.2 

71.7 

81.4 

86.2 

88.6 

86.7 

80.9 

74.0 

63.8 

51.8 

71.1 

Tryon^  No.  4 . 

1,100 

51.0 

50.7 

55.4 

68.0 

77.1 

81.4 

84.2 

82.9 

77.0 

70.4 

61.1 

48.5 

67.3 

-3.6 

-3.6 

-3.8 

-3.7 

-4.3 

-4.8 

-4.4 

-3.8 

-3.9 

-3.6 

-2.7 

-3.3 

-3.8 

Feet  for  1°  difference . 

306 

306 

289 

297 

256 

229 

250 

289 

282 

306 

407 

333 

289 

1  Base  station  above  sea  level;  summit  above  base. 

>  1913  missing. 

3  jqj3  siid  1914  missing 

<  The  datum  “Feet  for  1°  difference”  obviously  fails  of  any  physical  significance  when  the  temperature  differences  between  slope  stations  are  quite  small  .—Ed. 


Table  Id. — Monthly  and  annual  average  maximum  temperatures  at  the  two  stations  having  the  highest  and  lowest  elevations,  respectively , ^showing  the 

rate  of  decrease  with  elevation,  1913-1916. 


Stations. 

Eleva¬ 

tion 

(feet). 

Janu¬ 

ary. 

Febru¬ 

ary. 

March. 

April. 

May. 

June. 

July. 

Au¬ 

gust. 

Septem¬ 

ber. 

Octo¬ 

ber. 

Novem¬ 

ber. 

Decem¬ 

ber. 

An¬ 

nual. 

Tryon,  No.  1 . 

Highlands,  No.  5 . 

Number  of  feet  for  1°  difference . 

950 

4,075 

54.6 

42.7 
-11.9 

263 

54.3 

41.9 

-12.4 

252 

59.2 

43.6 

-15.6 

200 

71.7 

60.4 

-11.3 

277 

81.4 

70.8 

-10.6 

295 

86.2 

74.4 

-11.8 

265 

88.6 

76.5 

-12.1 

258 

86.7 

75.4 

-11.3 

277 

80.9 

69.2 

-11.7 

267 

74.0 

62.2 

-11.8 

265 

63.8 

54.6 

-9.2 

340 

51.8 

43.5 

-8.3 

377 

71.1 

59.6 

-11.5 

272 

Average  monthly  and  annual  maximum  temperature. — A 
discussion  of  Table  1,  which  latter  contains  the  record  of 
the  average  maximum  temperatures  at  the  respective 
stations,  will  now  follow.  The  differences  between 
the  readings  at  the  base  station  and  those  at  higher 
levels  in  each  group  can  be  had  by  simple  inspection. 
This  discussion  will  also  include  a  study  of  the  maximum 
temperature  during  selected  periods  of  clear  weather 
shown  in  T&bl©  In.  Th©  lnttor  tnbl©  hns  b©©n  pr©pnr©d 
in  order  that  the  reasons  for  the  variations  during  sun¬ 
shiny  weather  may  be  seen  and  understood. 

On  account  of  the  shortness  of  the  periods  included  in 
Table  la,  and  the  great  latitude  allowed  the  observers  in 
reading  the  temperatures  to  whole  degrees,  individual 


comparisons  between  the  respective  stations  on  the  slopes 
do  not  always  show  the  uniformity  expected.  Longer 
periods,  if  such  were  available,  would  be  more  satisfactory, 
as  the  inequalities  would  then  be  smoothed  out,  or,  at 
least,  questionable  or  unusual  values  would  not  stand  out 
so  prominently  as  in  a  short  period. 

Since  the  position  of  the  sun  relative  to  the  various 
slopes,  has  an  important  bearing  on  maximum  tempera¬ 
ture,  two  clear  periods  have  been  selected  in  Table  la, 
and  are  presented,  one  in  May,  1914,  when  the  sun  is  high 
in  the  heavens,  and  the  other  in  November,  1914,  when 
its  meridian  altitude  is  low. 

Before  going  into  the  discussion  of  the  individual 
tables  in  detail  it  might  be  well  first  to  understand  the 


26 


SUPPLEMENT  NO.  19. 


reasons  for  the  differing  amount  of  insolation  received 
during  sunshiny  weather  on  unit  areas  of  slopes  of  varying 
inclination  and  direction,  as  illustrated  by  figure  42. 

It  is  quite  apparent  from  a  glance  at  that  graph  that 
practically  equal  insolation  is  received  during  the  month 
of  June  on  both  north  and  south  facing  slopes,  as  shown 
by  the  areas  A,  B,  and  D,  the  degree  of  inclination  of  the 
slope  at  this  season,  when  the  sun  is  high  in  the  heavens, 
being  a  negligible  factor. 

However,  it  may  also  readily  be  seen  that  there  is  a 
considerable  difference  in  the  insolation  on  a  slope 
according  as  it  faces  north  or  south  during  the  month  of 
December,  when  the  meridian  altitude  of  the  sun  is  low, 
as  represented  by  the  areas  C,  E,  and  A.  This  is  because 
the  same  amount  of  insolation  is  spread  out  over  much 
greater  area  on  a  north-facing  slope  than  on  one  with  a 
southerly  exposure.  Likewise,  the  intensity  of  the  inso¬ 
lation  received  on  a  north-facing  slope  during  the  winter 


In  Table  la  there  is  shown  to  be  a  somewhat  greater 
decrease  in  maximum  temperature  with  elevation  during 
clear  weather  than  appears  in  the  general  average  in 
Table  1  embracing  all  weather  conditions,  and  this  is 
what  should  be  expected,  as  the  vapor  pressure  is  usually 
less  during  clear  weather.  Moreover,  Altapass  is  a 
regular  slope  and  the  exposures  of  the  various  stations 
are  quite  uniform.  There  is  a  certain  harmony  between 
the  variations  during  the  two  clear  periods,  especially 
between  the  two  lower  stations  and  that  at  the  summit. 

Asheville  (Table  1). — During  all  the  months  of  the 
ear  the  maxima  at  station  No.  3  average  lowest 
ecause  of  its  location  on  the  northerly  slope  close  to 
heavy  timber  to  the  south,  west,  and  east,  which  permits 
very  little  sunshine  in  the  vicinity  of  the  shelter  and 
keeps  it  in  a  heavy  shade.  As  the  slope  is  rather  steep 
northerly,  the  effective  rays  of  the  sun  are  at  a  minimum 
in  the  winter,  as  shown  in  Figure  42. 


months  will  vary  with  the  degree  of  inclination,  as  shown 
by  areas  C  and  E,  the  gentler  the  slope  the  more  con¬ 
centrated  the  insolation.  We  find,  then,  higher  maxima 
during  the  colder  months  on  a  southerly  slope  than  on  a 
northerly  one  simply  because  the  sun’s  rays  on  a  south¬ 
facing  slope  are  more  direct  and  therefore  more  effective. 

Average  Maxima  on  Individual  Slopes;  Also 
Maxima  During  Sunshiny  Periods — Altapass 
(Table  1). — There  is  apparently  little  seasonal  change 
in  the  differences  between  the  maxima  at  the  five  stations 
on  this  long  southeasterly  slope,  the  differences  for  the 
various  months  being  remarkably  uniform  throughout 
the  year.  The  maxima  at  station  No.  1  average  the 
highest  during  all  months,  and  the  readings  at  the  sum¬ 
mit  station,  No.  5,  1,000  feet  above,  the  lowest.  The 
slight  variation  in  these  differences  from  month  to  month 
is  due  to  change  in  shade  from  near-by  timber  and 
vegetation.  The  average  difference  for  the  four-year 
period  between  No.  1  and  No.  5  is  4.2°,  or  a  decrease  of 
1°  for  each  238  feet.  As  this  is  a  southeast  slope,  it  has 
considerable  sunshine,  especially  in  the  morning. 


The  maxima  average  highest  at  station  Nos.  1  and 
3a,  the  readings  being  slightly  lower  at  No.  3a  than  at 
No.  1  in  the  summer  months  and  slightly  higher  in  early 
spring  and  late  fall  months.  No.  3a  is  on  a  southerly 
slope,  but  the  timber  during  the  growing  season  screens 
the  sun  to  some  extent.  On  the  other  hand,  the  sun’s 
rays  are  more  direct  on  this  southerly  slope  at  No.  3a 
during  the  winter,  resulting  then  in  a  higher  maximum 
on  sunshiny  days  than  at  No.  1. 

As  might  be  expected,  the  maxima  at  station  No.  2a 
on  the  south  slope  average  higher  than  at  No.  2  on  the 
opposite  northerly  slope,  taking  the  year  as  a  whole, 
but  the  excess  is  gained  wholly  during  the  fall  and 
winter  months,  while  a  small  negative  difference  exists 
during  the  late  spring  and  early  summer  months  (see 
table  on  page  23).  The  reason  for  this  apparent  anomaly 
is  immediately  evident  upon  consideration  of  the  profile 
of  the  valley  (fig.  17)  and  the  varying  meridian  altitude 
of  the  sun  from  December  to  June.  When  the  sun 
reaches  its  lowest  meridian  altitude  in  December,  31° 
in  the  latitude  of  the  Carolina  mountain  region,  the 


THERMAL  BELTS  AND  ERUIT  GROWING  IN  NORTH  CAROLINA. 


27 


south-facing  slope  at  station  No.  2a  receives  about 
twice  as  much  insolation  over  a  given  area  as  No.  2. 
But  after  the  vernal  equinox,  as  the  sun  rises  higher 
and  higher,  this  difference  in  the  amount  of  heat  received 
becomes  such  a  negligible  quantity  that  it  may  be  dis¬ 
regarded  entirely,  and  it  is  found  that  the  maximum 
temperatures  are  then  practically  the  same  at  both 
stations.  In  June,  with  the  sun’s  rays  from  a  meridian 
altitude  of  78°,  the  insolation  on  both  slopes  is  about 
equal  in  amount,  but  at  No.  2a,  where  the  slope  is  steep 
and  faces  a  large  area  of  free  air,  the  unstable  equili¬ 
brium  of  the  surface  air  is  rapidly  relieved  by  interchange. 

Another  reason  for  the  relatively  high  maximum 
during  the  spring  and  summer  months  at  No.  2  on  the 
north  slope  is  the  fact  that  there  is  considerable  vegeta¬ 
tion  surrounding  the  station  which  serves  to  trap  the 
heated  air  while  the  location  on  the  north  facing  slope 
at  No.  2a  is  almost  bare  of  vegetation. 


Four-year  average  maxima,  Asheville,  Nos.  2  and  2a  and  3  and  3a, 
including  direction  of  slope  ana  elevation  above  the  base. 


January. 

February. 

March. 

April. 

May. 

June. 

July. 

August. 

September. 

October. 

N  ovember. 

December. 

j  Annual. 

No.  2,  N.,  155 
feet . 

49.4 

46.7 

51.2 

64.0 

74.8 

78.8 

81.1 

80.2 

74.8 

66.1 

56.9 

46.0 

64.2 

No.  2a,  S.,  155 

50.1 

47.7 

51.5 

63.9 

74.0 

78.2 

80.4 

80.2 

75.3 

67.2 

58.2 

47.3 

64.5 

Difference . 

+0.7 

+1.0 

+0.3 

-0.1 

-0.8 

-0.6 

-0.7 

0.0 

+0.5 

+  1.1 

+  1.3 

+  1.3 

+0.3 

No.  3,  N.,  380 

47.0 

44.9 

49. 61  63.0 

72.8 

75.9 

78.0 

76.8 

70.4 

62.4 

53.8 

43.6 

61.5 

No.  3a,  S.,  380 

51.0 

48.8 

52.9  66.3  75.6 

79.2 

81.2 

80.3 

74.8 

67.8 

60.6 

48. 3 

05.  0 

feet . 

Difference . 

+4.0 

+3.9 

+3.3|+3. 3+2.8 

+3.3 

+3.2 

+3.5 

+4.4 

+5.4 

+6. 8+4.7 

+4.1 

From  an  examination  of  this  table  it  is  evident  that  the 
maxima  at  No.  3  on  the  northerly  slope  are  lower  than 
those  at  No.  3a  with  a  south  exposure  during  all  months 
of  the  year,  the  greatest  difference,  6.S°,  occurring  m 
November  and  the  least  difference,  2.8  ,  in  May.  Duimg 
June,  when  the  meridian  altitude  of  the  sun  is  the  highest, 
practically  equal  insolation  prevails  on  these  two  lacing 
slopes  (see  fig.  42) .  However,  as  stated  previously,  there 
is  a  large  amount  of  shade  at  No.  3  as  compared  with  the 
conditions  in  the  vicinity  of  No.  3a,  and  this  effectually 
screens  the  sun’s  rays  from  the  former,  especially  m  the 
the  middle  of  the  day,  so  that  the  temperature  there  is 
prevented  from  reaching  as  high  a  point  as  at  No.  3a 
In  December,  with  the  sun  at  a  low  meridian  altitude,  the 
question  of  shade,  although  still  a  factor,  is  not  so  impor¬ 
tant  as  the  amount  of  effective  insolation  received  at 
these  two  points.  Owing  to  its  position  on  the  northeriy 
slope  and  timber  to  the  east  and  west  No.  3  at  this  time 
of  the  year  is  cut  off  from  any  rays  of  the  sun,  while  No.  3a 
on  the  opposite  slope  receives  more  effective  insolation  m 
comparison  with  that  received  at  No.  3  than  it  did  111  June. 

For  the  same  reason  outlined  on  a  previous  page  m  the 
comparison  between  the  maxima  at  No.  2  and  No.  2a,  the 
months  in  which  the  least  and  greatest  differences  occur 
between  Nos.  3  and  3a  are  May  and  November,  iespec- 
tively  instead  of  June  and  December,  as  would  be  ex¬ 
pected  were  the  angle  of  the  sun  s  rays  the  only  factoi. 
P  Figure  43  illustrates  the  effect  of  shade  m  reducing the 

mirlnicrht  October  30  to  noon  November  1,  1J13,  tne 
maximum  temperature  on  the  southerly  slope  was  each 
dLv  macticallv  13°  higher  than  on  the  slope  opposite. 
tVe  fig£e are  also  shown  the  curves  of  temperature 


30442 — 23 - 3 


for  the  same  period  for  the  stations  Nos.  2  and  2a  on  these 
slopes,  but  here  we  have  no  contrast  of  sunshine  and 
shade,  as  at  the  upper  stations,  but  the  effect  only  of 
northerly  and  southerly  inclination  and  varying  amounts 
of  vegetation.  The  maxima  on  the  southerly  slope  at 
No.  2a  rise  to  a  higher  point  than  at  No.  2,  but  the  differ¬ 
ence  is  only  2°  or  3°.  In  the  warmer  months  of  the  year, 
when  the  sun  is  more  nearly  overhead,  there  is  no  appre¬ 
ciable  difference  between  these  two  stations  on  days  of 
sunshine. 

In  the  comparison  in  Table  la,  the  variation  in  maxi¬ 
mum  temperature  at  the  two  stations  on  the  northerly 
slope,  as  compared  with  those  at  the  base  and  on  the 
southerly  slope  during  the  selected  periods  of  clear 
weather 'in  May  and  November,  is  quite  marked,  for  reasons 
similar  to  those  already  stated. 


Blantyre  (Table  1). — Disregarding  the  summit  station, 
the  maximum  temperature  on  this  slope  decreases  uni¬ 
formly  with  elevation.  The  average  difference  between 
the  summit  and  the  base  is  very  slight,  and  m  some 
months  the  average  at  the  summit  is  higher.  This  is  due 
doubtless  to  the  fact  that  there  is  more  effective 'insola¬ 
tion  and  denser  vegetation  at  the  summit  station  No.  4 
than  at  No.  1,  which  is  really  on  a  small  bench  on  a 
o-radual  northerly  slope,  a  slight  distance  above  the 
valley  floor.  As  there  is  no  month  in  which  the  average 
difference  between  these  two  stations  approaches  the 
normal  rate,  there  must  be  a  factor  or  factors  working 
durino-  the  entire  year  to  prevent  the  temperature  at 
No.  l°from  reaching  higher  maxima.  The  forest  growth 
above  and  to  the  south  of  No.  1  shades  this  station  during 
much  of  the  time;  in  the  spring  and  summer  on  account 
of  the  foliage  on  the  trees,  and  in  the  fall,  even,  because 
the  trees,  notwithstanding  the  diminished  foliage,  otter 
obstruction  sufficient  to  modify  considerably  the  Gleet 
of  the  sun’s  heat,  although  the  condition  of  shade  at  this 
point  is  far  from  being  as  pronounced  as  at  station  No.  3, 
Asheville.  In  the  winter  the  low  altitude  of  the  sun 
becomes  an  additional  factor,  while  m  the  summer  the 
excessive  cloudiness  in  the  early  afternoon  aids  m  cutting 
down  the  difference  in  the  maxima  between  Nos.  1  and  4. 

The  average  difference  between  the  maxima  at  Nos. 
1  and  2  is  0.9°  for  an  ascent  of  300  feet,  and  this  is  about 

what  should  be  expected.  . 

Station  No.  3  has  a  lower  average  maximum  than  any 
other  of  the  Blantyre  stations  during  the  whole  year, 
because  of  the  fact  that  the  slope  is  northerly  and  steep 
and  is  ineffectively  heated  by  the  sun  s  rays  The  differ¬ 
ences  between  Nos.  1  and  4  and  between  3  and  4  are 


28 


SUPPLEMENT  NO.  19. 


abnormal.  As  No.  4  is  located  on  the  summit  and 
receives  more  effective  insolation,  as  previously  stated, 
the  maxima  at  that  station  are  rather  high,  and  this  is 
the  case  especially  in  the  fall,  when  the  number  of  clear 
days  is  the  greatest. 

During  the  clear  period  in  May,  as  shown  by  Table  la, 
station  No.  2  has  an  average  of  1.1°  higher  than  No.  1, 
and  this  is  largely  because  the  former  is  located  in  a  sag 
or  gully  where  tne  warm  air  is  trapped  by  the  near-by 
vegetal  growth,  whereas  No.  1  is  on  a  flat  bench  with 
but  little  vegetation  in  the  vicinity,  besides  being  in  the 
shade  much  of  the  time,  as  stated  above.  This  excess 
of  1.1°  at  No.  2  over  No.  1  is  in  marked  contrast  with  the 
four-year  average  deficiency  of  0.9°  as  shown  in  Table  I, 
and  this  is  because  the  latter  average  includes  both  clear 
and  cloudy  days.  No  4  also  is  Iff  "her,  while  No.  3  on  the 
northwest  slope  has  naturally  the  lowest  maximum  in  the 
entire  group. 

During  the  November  period  (Table  la)  station  No.  2 
shows  a  more  nearly  normal  rate  of  decrease  as  compared 
with  station  No.  1,  as  in  this  month  the  vegetation  in  the 
vicinity  of  No.  2  is  not  a  factor.  Station  No.  3  shows  an 
an  increase  in  the  difference  between  it  and  No.  1  in 
November  as  compared  with  May,  and  this  is  no  doubt 
due  to  the  more  effective  insolation  at  No.  1  than  at  No.  3 
during  this  month,  when  the  meridian  altitude  of  the 
sun  is  low,  while  the  effect  of  shade  at  No.  1  in  November 
as  compared  with  the  station  No.  4  on  the  summit  is 
responsible  for  the  variation  in  the  difference  shown  in 
Table  la  between  these  two  locations. 

Blowing  Rock  (Table  1). — In  comparing  the  maximum 
temperatures  at  Blowing  Rock,  it  should  be  understood 
that  there  are  two  groups  of  stations  on  different  slopes 
about  one-half  mile  apart,  stations  Nos.  1  and  2  being 
located  in  the  China  orchard  and  Nos.  3,  4,  and  5  in  the 
Flat  Top  orchard. 

The  highest  maxima  occur  at  No.  1,  although  there  is 
very  little  difference  between  this  station  and  No.  2. 
No.  1  is  by  no  means  a  base  station,  as  both  it  and  No.  2 
are  on  a  rather  steep  southerly  slope  in  the  China  orchard. 
No.  2  receives  more  effective  insolation  than  No.  1,  espe¬ 
cially  in  the  winter;  hence  this  slight  average  difference 
between  the  stations,  0.3°,  although  the  difference  in 
elevation  is  450  feet.  The  maxima  m  the  China  orchard 
are  uniformly  higher  than  those  recorded  at  stations 
Nos.  3,  4,  and  5  in  the  Flat  Top  orchard  because  of  the 
difference  in  local  exposure.  Nos.  1  and  2  are  situated 
on  a  steep  narrow  slope  with  high  inclosing  sides,  which 
tend  to  prevent  a  free  circulation  of  air,  and  thus  aid  in 
producing  relatively  high  maxima,  while  Nos.  3,  4,  and 
5  have  a  freer  exposure,  as  they  are  located  on  the  slope  of 
a  huge  amphitheater-shaped  basin  with  an  opening  to 
the  southeast.  (See  fig.  30.) 

During  the  period  of  clear  weather  in  May  (see  Table 
la)  the  difference  between  the  values  at  Nos.  1  and  2, 
— 1.8°,  is  about  what  should  be  expected,  while  there  is 
a  difference  of  only  +0.1°  in  the  November  period.  This 
variation  is  undoubtedly  due  to  the  fact  that  in  the  winter 
there  is  more  effective  insolation  at  No.  2  than  at  No.  1, 
while  in  the  summertime  the  normal  rate  of  decrease  be¬ 
tween  the  two  points  prevails,  as  the  amount  of  insolation 
received  at  Nos.  1  and  2  is  practically  equal.  For  the 
same  reason  there  is  a  seasonal  variation  in  the  rate  of 
decrease  between  Nos.  2  and  3  in  that  No.  2  averages  0.9° 
higher  in  the  May  period  and  2.3°  higher  in  the  November 
period. 

Bryson  (Table  1). — The  differences  between  the  max¬ 
ima,  at  Bryson  do  not  vary  materially  for  the  entire 
period,  but  there  is  a  remarkable  seasonal  variation  noted 


between  Nos.  1  and  3,  the  base  and  the  summit  stations. 
Beginning  with  February,  the  temperature  at  No.  3 
exceeds  that  at  No.  1,  culminating  in  the  month  of  April 
with  a  four-year  average  excess  of  3.7°.  With  the 
advance  of  the  season,  the  difference  gradually  becomes 
less  and  less  until  July,  when  it  becomes  a  deficiency 
which  increases  to  an  average  of  2°  in  December.  This 
change  is  quite  uniform  throughout  each  of  the  four 
years  of  record  and  may  be  due  to  the  rapid  growth  of 
vegetation  in  the  vicinity  of  No.  3  in  the  early  spring, 
although  tlxis  could  not  be  considered  a  factor  as  early 
as  February.  However,  the  excess  in  maximum  tempera¬ 
ture  at  No.  3  does  not  begin  until  toward  the  close  of 
that  month,  the  vegetation  there  doubtless  reaching 
its  maximum  density  in  May.  The  peculiar  situation 
at  No.  3  is  probably  due  to  some  extent  at  least  to  the 
surrounding  vegetation  and  timber  in  the  vicinity,  which 
trap  the  warm  air.  The  condition  is  purely  local,  and 
the  temperature  oscillates  considerably  on  sunshiny 
days  during  the  months  in  which  the  excess  is  noted, 
especially  in  the  spring. 

The  difference  in  height  between  the  summit  and  the 
base  being  570  feet,  the  average  decrease  in  temperature 
of  2°,  as  noted  in  December,  does  not  differ  much  from  the 
normal  rate  in  strong  contrast  with  the  excess  of  3.7°, 
noted  in  April.  The  average  excess  at  the  summit  in 
April,  1914,  amounted  to  4.6°,  while  the  average  deficiency 
in  September,  1916,  was  3.9°. 

Of  course,  where  sunshine  is  a  principal  factor  in 
governing  a  variation,  the  monthly  average  differences 
should  depend  upon  the  relative  frequency  of  sunshiny 
days,  the  greater  the  amount  of  sunshine  the  more  marked 
the  excess  or  deficiency  as  the  case  may  be,  while  in 
months  with  an  excess  of  cloudiness  the  differences  in 
the  maximum  temperature  should  depend  almost  entirely 
upon  elevation.  For  instance,  in  July,  1916,  a  cloudy 
month,  the  average  deficiency  at  No.  3  as  compared 
with  No.  1  was  1.8°,  while  in  July,  1913,  a  sunshiny  month, 
the  average  excess  at  the  summit  station  was  0.3°. 

The  variation  in  maximum  temperature  between  the 
the  northerly  and  southerly  slopes  at  both  Asheville 
and  Bryson  is  consistent  in  the  various  months  of  the 
year,  as  shown  by  the  table  below,  in  that  the  excess  on 
the  southerly  slope  is  greatest  at  both  places  during 
the  winter  season,  when  the  sun  is  farthest  south,  with 
the  most  insolation  on  a  south-facing  exposure.  The 
excess  on  the  northerly  slope  is  greatest  at  Asheville 
from  May  to  July,  inclusive,  and  at  Bryson  from  July 
to  September,  but  at  Bryson  the  differences  in  the  summer 
are  very  slight.  This  table  indicates  the  mean  differences 
by  months  for  stations  No.  2  and  No.  2a  at  both  Asheville 
and  Bryson.  The  grades  of  these  slopes  are  not  the 
same,  so  that,  of  course,  the  comparison  will  serve  only 
in  a  general  way. 


Four-year  average  maxima,  Asheville  and  Bryson,  Nos.  2  and  2a, 
including  direction  of  slope  and  elevation  above  the  base. 


January. 

February. 

March. 

April. 

May. 

June. 

July. 

August. 

September. 

October. 

November. 

December. 

Annual. 

Asheville: 

2,  N.,  155 
feet . 

49.4 

46.7 

51.2 

64.0 

74.8 

78.8 

81.1 

80.2 

74.8 

66.1 

56.9 

46.0 

64.2 

2a,  S.,  155 
feet . 

50.1 

47.7 

51.5 

63.9 

74.0 

78.2 

80.4 

80.2 

75.3 

67.2 

58.2 

47.3 

64.5 

Difference. . 

+0.7 

+  1.0 

+0.3 

-0.1 

-0.8 

-0.6 

-0.7 

0.0 

+0.5 

+1.1 

+1.3 

+  1.3 

+0.3 

Bryson: 

2,  N.,  385 
feet . 

50.6 

51.1 

54.1 

68.9 

79.4 

82.8 

84.8 

84.2 

79.2 

70.4 

59.8 

46.4 

67.6 

2a.  S.,  385 
feet . 

52.3 

52.2 

55.1 

69.8 

79.7 

82.9 

84.7 

83.8 

79.0 

71.4 

61.6 

48.2 

68.4 

Difference. . 

+  1.7 

+1.1 

+  1.0 

+0.9 

+0.3 

+0.1 

-0.1 

-0.4 

-0.2 +1.0 

+1.8 

+1. 8 

+0.8 

THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 


Cane  River  (Table  1). — The  maxima  do  not  decrease 
here  with  elevation  through  the  various  months  of  the 
year  with  any  regularity.  The  readings  at  station  No. 
3,  400  feet  above  the  base,  are  unusually  low,  and  those 
at  No.  4  relatively  high;  in  fact,  for  the  four-year  period 
No.  4  averages  0.4°  higher  than  at  No.  3,  which  is  700 
feet  lower  down. 

No.  3,  which  is  in  a  cove-like  depression  on  a  north 
slope,  with  Rocky  Knob  towering  above  to  the  south 
and  timber  in  most  directions  except  southeast,  is  not 
only  cut  off  from  sunshine  during  much  of  the  morning 
and  afternoon,  but  the  slanting  rays  of  the  sun  on  the 
steep  slope  are  ineffective  in  raising  the  surface  tempera¬ 
ture.  This  condition,  of  course,  is  most  marked  during 
the  sun’s  lowest  meridian  altitude,  and  the  difference  in 
insolation  as  reflected  in  the  daytime  temperatures  at 
Nos.  3  and  4  is  well  shown  in  figure  44. 

A  seasonal  variation  is  noted  between  No.  3  and  No.  1 
in  that  the  maximum  at  No.  3  is  much  lower  than  that 
at  No.  1  in  the  colder  months  of  the  year,  and  we  would 
expect  on  this  account  to  find  the  greatest  average 
monthly  difference  between  the  maxima  at  No.  1  and 
No.  3  in  December,  but  this  actually  occurs  in  October 
and  November,  because  of  the  large  number  of  sunshiny 
days  in  those  months.  During  the  month  of  October, 
1914,  the  average  difference  between  the  maxima  at 
Nos.  1  and  3  on  8  cloudy  days  was  1.7°,  while  on  17 
clear  days  the  average  difference  was  7.6°.  The  greatest 
difference  on  any  cloudy  day  was  5°,  while  on  one  clear 
day  the  difference  was  13°  and  on  a  majority  of  the  17 
days  the  differences  were  8°  or  more. 

Kow,  taking  the  month  of  May,  1914,  a  month  unlike 
October  in  that  the  altitude  of  the  sun  is  then  higher, 
when  its  rays  reach  into  the  cove  at  No.  3,  thus  producing 
more  equal  insolation  at  Nos.  1  and  3  than  during  October 
when  the  altitude  of  the  sun  is  lower,  we  find  an  average 
difference  of  1.7°  between  Nos.  1  and  3  for  7  cloudy  days, 
exactly  the  same  as  during  a  period  of  cloudy  weather  in 
October,  1914;  while  on  18  clear  days  in  May  the  average 
difference  is  only  1.5°,  compared  with  an  average  differ¬ 
ence  of  7.6°  in  a  period  of  clear  weather  in  October,  1914. 
On  1  cloudy  day  in  May,  1914,  the  extreme  difference  of 
5°  was  noted,  while  on  no  one  of  the  18  clear  days  was 
there  a  difference  greater  than  3°. 

Therefore,  in  the  summer  time,  when  the  sun  is  highest 
and  the  rays  strike  directly  down  into  the  cove  at  No.  3, 
the  differences  between  the  maxim  at  Nos.  1  and  3  are 
small  as  compared  with  those  in  the  colder  months  of 
the  year.  If  June  and  December  were  as  clear  as  May 
and  October,  the  least  and  greatest  ranges  between  the 
differences  at  Nos.  1  and  3  would  be  found  in  the  former 
months,  but  the  latter  months  are  taken  simply  because 
of  the  greater  number  of  sunshiny  days. 

The  average  decrease,  2.6°,  in  maximum  temperature 
for  the  four-year  period  from  No.  1  to  summit  station 
No.  4  for  an  elevation  of  1,100  feet  is  at  the  rate  of  1° 
for  423  feet.  No.  4  is  located  on  a  knob  with  dense 
timber  below  on  all  surrounding  slopes,  except  on  the 
east  side,  and  a  vast  amount  of  heated  air  is  trapped  in 
the  upper  portion  of  the  timber,  and  this  heat,  together 
with  that  radiated  from  the  surface  of  the  foliage,  is  felt 
on  the  knob.  There  is,  moreover,  a  clearing  around  the 
shelter,  permitting  free  exposure  to  sunshine  at  all  times, 
although  small  brush  covers  the  ground. 

In  Figure  44  are  temperature  curves  representing 
Nos.  1,  3,  and  4,  Cane  River,  for  the  two  days  January 
4-5,  1916,  which  show  the  great  excess  in  day  temperature 
during  sunshine  at  Nos.  1  and  4  as  compared  with  that 
at  No.  3.  On  the  4th,  a  clear,  calm  day,  the  maximum 


at  No.  3  was  12°  lower  than  that  at  Nos.  1  and  4,  where 
the  maxima  were  unusually  high,  being  intensified  by 
the  existing  calm,  while  on  the  5th,  a  cloudy  day,  the 
differences  in  maxima  were  not  so  marked. 

Ellijay  (Table  1). — The  maxima  at  Ellijay  show 
greater  uniformity  than  perhaps  any  other  group  of 
stations  not  only  in  the  four-year  averages  but  in  the 
individual  months.  With  an  elevation  of  the  summit 
station  above  the  base  of  1,760  feet  on  this  northerly 
slope  there  is  an  average  decrease  in  maximum  tempera¬ 
ture  of  5.8°,  approximately  1°  for  each  303  feet.  No.  4, 
at  an  elevation  of  1,240  feet  above  No.  1,  shows  the 
only  irregularity,  doubtless  because  of  the  configuration 
of  the  slope  and  the  near-by  timber,  which  shut  off  the 
sunshine  more  than  at  the  other  stations,  especially  in 
the  winter  months.  Tins  slope  and  that  at  Altapass  are 
the  most  regular  of  all  the  slopes. 

The  variation  in  the  maximum  temperature  during 
the  May  clear  period  (Table  la)  shows  a  comparatively 
lower  reading  at  station  No.  3  and  a  higher  one  at  No.  4 
than  is  indicated  by  the  four-year  averages.  In  this 
case  the  readings  of  all  the  stations  are  consistent  except 
that  at  No.  3,  which  for  some  reason  is  not  in  harmony 
with  the  averages  at  other  stations. 


Fig.  44. — Thermograph  traces,  January  4-5, 1916,  stations  Nos.  1,  3,  and  4,  Cane  River. 


The  Ellijay  stations,  located  as  they  are  on  a  northerly 
slope,  naturally  have  lower  day  temperatures  as  com¬ 
pared  with  the'base  during  the  month  of  November  than 
in  May,  and  this  fact  is  brought  out  by  the  figures  in 
Table  la,  with  the  exception  of  those  at  station  No.  3. 

Globe  (Table  1).— In  this  group  of  three  stations  the 
maximum  readings  do  not  show  a  decrease  approaching 
the  normal  rate.  Station  No.  3,  at  an  elevation  of 
1,000  feet  above  No.  1,  has  a  mean  maximum  only  2.2° 
lower  than  No.  1,  approximately  1°  for  each  455  feet. 
This  slight  decrease  is  doubtless  because  No.  3,  the 
summit  station,  being  located  on  an  arm  of  Grandfather 
Mountain,  receives  a  much  greater  share  of  insolation 
than  the  base.  The  maxima  at  No.  2  on  the  easterly 
slope,  only  300  feet  above  the  base,  averages  1.8°  lower 
than  No.  1,  this  large  difference  being  due  to  the  shutting 
off  of  the  sun  at  No.  2  by  surrounding  timber  early  in  the 
afternoon,  especially  in  the  late  tall  and  winter,  as 
stated  in  description  of  Figure  35. 

In  the  comparison  in  Table  la,  the  effect  of  sunshine 
on  elevated  sections  is  shown  as  compared  with  those 
lower  down. 

A  marked  seasonal  variation  between  the  maxima 
observed  at  Nos.  2  and  3  is  brought  out  strongly  by  the 
figures  in  Table  la.  During  the  period  in  November 


30 


SUPPLEMENT  NO.  19. 


No.  3  averages  3.3°  higher  than  No.  2,  located  700  feet 
below,  while  in  May  it  averages  higher  by  but  0.1°. 

Gorge  (Table  1). — At  the  summit  station  of  Gorge, 
with  an  elevation  of  1,040  feet  above  the  base,  the  maxi¬ 
mum  averages  3.2°  lower  than  at  the  base,  approxi¬ 
mately  1°  difference  for  each  325  feet.  The  average 
differences  for  July,  September,  and  October  all  exceed 
4°,  while  in  January  and  December  the  average  differ¬ 
ences  are  as  low  as  2°.  This  variation  is  due  largely  to 
the  fact  that  the  sun’s  rays  are  far  more  effective  in  the 
warmer  months  than  in  the  cold  months  of  December 
and  January  at  the  base  of  a  northeasterly  slope  on  which 
No.  1  is  located  as  compared  with  the  summit.  In  the 
latter  months,  when  the  sun’s  rays  strike  this  north¬ 
easterly  slope  obliquely,  the  maximum  readings  at  all 
stations  on  the  slope,  including  No.  1,  more  nearly 
approximate  the  readings  at  the  summit.  This  is  brought 
out  by  the  figures  in  the  tables  and  should  be  compared 
with  the  monthly  variation  on  the  southeasterly  slope 
at  Altapass,  for  instance,  which  shows  no  such  variation 
in  maximum  temperature  differences  at  its  stations  in 
the  different  months  of  the  year.  In  fact,  at  Altapass 
the  maximum  temperature  in  the  summer  at  the  summit 
averages  lower  than  the  base  station  by  the  same  amount 
as  during  the  winter.  The  average  difference  of  4.2° 
for  the  four  years  at  Altapass  for  a  difference  in  elevation 
of  1,000  feet  is  even  somewhat  exceeded  in  the  winter 
months,  January  showing  a  difference  of  4.3°  and  Febru¬ 
ary,  4.6°,  while  at  Gorge,  for  a  difference  in  elevation  of 
1,040  feet  between  the  base  and  the  summit,  the  average 
four-year  difference  is  3.2°,  but  the  January  and  February 
months  have  differences  of  only  2°  and  2.6°,  respectively. 
These  figures  indicate  strongly  the  effect  of  the  direction 
of  the  slope  on  the  maximum  temperature  as  modified 
by  the  season,  which  fact  is  also  brought  out  prominently 
in  the  comparisons  between  the  northerly  and  southerly 
slope  stations  at  Asheville  and  Bryson.  (See  the  dis¬ 
cussion  on  those  stations.) 

The  rates  of  decrease  in  maximum  temperature,  1.1° 
between  Nos.  1  and  2  at  Gorge  for  a  difference  in  elevation 
of  290  feet  and  2.6°  between  Nos.  1  and  3  for  a  difference 
in  elevation  of  615  feet,  are  somewhat  above  the  average, 
but  this  is  not  strange,  especially  as  compared  with  the 
situation  at  No.  5,  because  Nos.  2  and  3  are  shut  off  from 
sunshine  during  a  considerable  portion  of  the  day.  The 
rate,  however,  at  No.  4  shows  a  smaller  value,  2.8°  for  840 
feet,  or  1°  for  300  feet.  But  this  statement  needs  some 
qualification.  No.  4  was  located  during  1913  and  1914  on 
a  north  slope  at  an  elevation  of  840  feet  above  the  base, 
and  during  1915  and  1916,  on  a  northeast  slope  at  the 
same  elevation.  The  maxima  were  much  higher  at  the 
first  location  than  at  the  second  as  compared  with  the 
base  station,  the  average  two-year  difference  between  the 
old  No.  4  and  No.  1  and  between  the  new  No.  4  and  No.  1 
being  1.8°  and  3.8°,  respectively.  There  was  a  better  ex¬ 
posure  to  insolation  at  the  old  location,  as  the  shelter  was 
located  on  a  small  ridge  with  downward  slopes  on  either 
side  to  west  and  east,  in  the  midst  of  surrounding  vegeta¬ 
tion  such  as  is  likely  to  be  found  in  any  neglected  apple 
orchard;  and  on  sunshiny  days  the  radiation  of  heat 
from  this  vegetation  was  relatively  large.  The  maxima 
in  1915  and  1916,  however,  were  low  as  compared  with 
those  at  the  old  location  in  1913  and  1914,  as  the  station 
did  not  have  such  a  free  exposure  to  sunshine  in  the 
later  period  and  there  was  not  as  much  vegetation  sur¬ 
rounding  the  shelter.  Fig.  36  shows  the  locations  of  the 
old  and  the  new  No.  4  stations,  respectively. 

The  comparison  in  Table  la  for  the  clear  periods  will 
serve  to  bring  out  more  prominently  the  variation  be¬ 


cause  of  sunshine.  During  the  May  period  the  maxima 
were  really  lower  at  all  the  stations  above  the  base  than 
we  should  expect,  the  low  reading  at  No.  3  in  the  cove  at 
an  elevation  of  615  feet  above  the  base  being  the  most 
pronounced. 

As  a  rule  during  November  the  maxima  on  the  slope 
are  not  so  low  as  compared  with  the  base  as  in  May,  and 
this  is  probably  because  of  the  greater  amount  of  sun¬ 
shine  during  months  when  the  foliage  has  fallen  from  the 
trees.  This  is  clearly  the  case  at  station  No.  4,  which, 
although  located  on  a  northerly  slope  in  1914,  has  at  the 
same  time  a  free  east  and  west  exposure,  the  location  of 
the  shelter  being  on  a  ridge  or  hogback. 

Hendersonville  (Table  1). — The  maximum  at  the  sum¬ 
mit  averages  3.2°  lower  than  at  the  base  station  for  a 
difference  in  elevation  of  750  feet,  a  rate  of  1°  for  each 
234  feet,  and  this  does  not  seem  to  be  due  so  much  to  the 
fact  that  No.  4  is  low  as  it  is  that  No.  1  is  rather  high. 
The  difference  is  quite  marked  between  Nos.  1  and  2,  2.1° 
for  450  feet,  but  the  decrease  between  Nos.  2,  3,  and  4 
is  smaller  and  quite  regular.  The  maximum  at  No.  1 
reaches  a  high  point  on  days  of  sunshine,  as  it  is  located 
in  a  pocket  surrounded  by  trees  on  all  sides  except  to  the 
southeast,  thus  trapping  the  air  and  preventing  free 
circulation. 

The  decrease  in  maximum  temperature  with  elevation 
during  the  clear  period  in  May,  1914,  as  shown  by  Table 
la,  is  somewhat  greater  between  Nos.  3  and  4  than  the 
four-year  average  decrease  and  less  between  stations 
Nos.  2  and  1,  and  this  variation,  as  well  as  that  between 
the  May  and  November  clear  periods,  is  due  to  the  effect 
of  wind  direction.  During  the  week  in  May  the  weather 
was  characterized  by  light  variable  winds,  mostly  south¬ 
erly  with  frequent  calms,  while  in  the  period  in  the  fall 
the  winds  were  light  to  moderate  northwesterly.  The 
small  average  difference  between  the  maxima  at  Nos.  1 
and  2  in  May  is  accounted  for  by  the  fact  that  during 
this  period  with  southerly  winds  No.  2,  being  located  in 
a  basin  protected  by  a  ridge  to  the  south,  has  relatively 
high  maxima.  In  fact,  high  temperatures  are  observed 
at  this  location  during  periods  of  calm  also,  as  there  is  no 
interchange  of  air  between  the  saucer-shaped  depression 
where  No.  2  is  situated  and  the  free  air  outside.  In 
November,  with  light  to  moderate  northwest  winds,  a 
circulation  is  produced  at  No.  2  as  this  station  is  not  then 
rotected  from  such  winds,  which  condition  prevents 
igh  maxima  as  compared  with  No.  1,  where  the  ques¬ 
tion  of  wind  direction  and  velocity  is  not  a  factor.  For 
this  same  reason  station  No.  3  averages  1.4°  lower  than 
No.  2  in  May  and  0.1°  higher  in  November.  It  is  there¬ 
fore  apparent  that  No.  2  has  relatively  high  maxima  in 
the  spring  and  relatively  low  maxima  in  November, 
during  both  periods  the  wind  direction  not  being  a  factor 
at  either  No.  1  or  No.  3.  In  other  words,  Nos.  1  and  3 
are  what  might  be  termed  “constants”  and  No.  2  the 
“  variable.” 

This  effect  in  wind  direction  is  strikingly  shown  by  the 
daily  maximum  readings  at  Hendersonville  on  three  suc¬ 
cessive  days  in  November,  1914,  and  the  following  table 
will  serve  to  illustrate  the  differences  in  maximum  tem¬ 
peratures  under  varying  wind  directions  and  velocities. 


Date. 

Maximum  tempera¬ 
tures. 

Wind  direction  and  velocity. 

No.  1. 

No.  2. 

No.  3. 

Nov.  23,  1914 . 

53 

46 

47 

Light  northwest  winds. 

Nov.  24,  1914 . 

48 

47 

48 

Do. 

Nov.  25,  1914 . 

61 

56 

57 

Do. 

THERMAL  BELTS  AND  FRUIT 

Highlands  (Table  1).— Stations  Nos.  1  and  2- are  in  the 
oatulah  orchard  under  conditions  much  unlike  those  ob¬ 
taining  m  the  Waldheim  orchard  2  miles  distant,  where 
3>  and  5  are  located.  While  the  maxima  at  No.  2, 
feet  an oye  No.  1,  should,  because  of  elevation,  average 
slightly  lower,  the  four-year  mean  is  0.6°  higher,  doubt¬ 
less  because  of  the  radiation  of  heat  from  Mount  Satulah 
the  immense  rock  which  stands  to  the  north  and  northeast 
immediately  above.  This  temperature  excess  at  No.  2 
over  No.  1  is  greatest  in  the  winter,  when  the  sun  is  in  the 
south  and  its  rays  more  directly  strike  the  side  of  the  rock 
above  No.  2.  Moreover,  No.  2  is  located  in  an  orchard 
in  the  midst  of  rather  high  grass  and  fruit  trees,  the 
headed  air  being  trapped  by  the  surrounding  vegetation, 
while  No.  1  is  over  comparatively  bare  soil.  On  many 
sunshiny  days  the  excess  in  maximum  temperature  at 
No.  2  is  large,  while  during  periods  of  cloudiness  and  pre¬ 
cipitation  No.  2  averages  lower  than  No.  1. 

During  the  month  of  December,  1914,  when  the  average 
maximum  temperature  at  No.  2  exceeded  that  at  No. 'l 
by  3.5°,  the  average  excess  at  No.  2  on  nine  days  with 
sunshine  was  5.3°,  while  on  nine  days  without  sunshine 
the  average  was  2.6°.  On  one  clear  quiet  day  No.  2 
recorded  a  maximum  of  45°,  while  No.  1  recorded  35°,  a 
large  difference,  considering  the  short  distance  between 
the  two  stations.  During  July,  1916,  a  month  with  ex¬ 
cessive  precipitation  and  much  cloudy  weather,  the 
the  average  difference  between  the  maxima  at  Nos.  1  and 
2  was  1.0°,  No.  2  in  this  case  averaging  lower  than  No.  1. 
In  July,  1914,  a  month  with  little  precipitation  and  much 
sunshine,  No.  2  averaged  1.5°  higher  than  No.  1. 

The  rate  of  decrease  in  maxima  between  No.  1  in  the 
Satulah  orchard  and  No.  3,  the  base  station  in  the  Wald¬ 
heim  orchard,  1.9°  for  325  feet,  is  greater  than  the  normal 
rate,  doubtless  because  of  the  better  exposure  to  insola¬ 
tion  at  No.  1  as  compared  with  that  at  No.  3.  However, 
the  variation  between  Nos.  3  and  4,  0.6°  for  200  feet,  is 
ractically  normal.  But  No.  5,  200  feet  above  No.  4, 
as  actually  a  higher  average  maximum  than  No.  4  by 
0.2°  for  the  four-year  period.  Although  both  stations 
are  on  a  slope,  the  slope  is  steeper  at  No.  4  than  at  No.  5, 
and  therefore  the  maxima  at  the  latter  would  more  nearly 
approach  those  found  over  level  places.  No.  4  has  thus 
a  freer  exposure  than  No.  5  because  of  the  above  fact 
and  also  because  No.  5  is  protected  on  the  west  and  south 
by  forest  growth,  which  is  not  found  around  No.  4.  The 
excess  in  average  maximum  temperature  at  No.  5  over 
No.  4  is  due  wholly  to  the  gain  made  on  days  of  sunshine, 
the  readings  being  actually  lower  on  cloudy  days. 

The  variation  at  Highlands  during  the  selected  period 
of  sunshine  in  May  shown  in  Table  la  is  rather  irregular, 
but  conforms  to  the  statements  in  foregoing  paragraphs, 
and  the  variation  in  the  November  perioclis  much  the  same 
as  in  May. 

Mount  Airy  (Table  1). — The  maxima  average  lower 
from  the  base  to  the  summit,  but  the  range  in  elevation  at 
Mount  Airy,  of  course,  is  not  great.  There  are  differences 
of  0.9°  and  1.1°  between  Nos.  1  and  2  on  the  west  slope 
and  between  Nos.  1  and  3  on  the  east  slope,  respectively. 
Both  slope  stations  are  160  feet  above  the  base,  while  the 
decrease  in  temperature  between  Nos.  1  and  the  summit 
station,  No.  4,  for  a  difference  in  elevation  of  360  feet 
is  1.6°. 

Station  No.  1  averages  rather  high  in  comparison  with 
the  other  stations  because  of  its  exposure  on  a  broad 
bench,  where  there  is  a  large  amount  of  radiating  surface. 
No.  2,  on  the  west  slope  at  an  elevation  of  160  feet  above 
the  base,  averages  for  the  four-year  period  0.2°  higher  than 
No.  3  at  the  same  elevation  on  the  east  slope,  and  it  is 


GROWING  IN  NORTH  CAROLINA.  31 

found  to  be  generally  the  case  that  the  average  maxima 
on  the  west  side  are  higher.  Moreover,  the  excess  at  No. 
2  over  No.  3  is  largely  in  the  warmer  season  of  the  year,  as 
shown  by  the  following  table,  which  gives  the  averages 
and  differences  for  the  four-year  period  for  the  two 
stations: 


Four-year  average  maxima,  Mount  Airy,  Nos.  2  and  3,  including  direc¬ 
tion  of  slope  and  elevation  above  the  base. 


January. 

February. 

1  March. 

April. 

May. 

June. 

July. 

August. 

September. 

October. 

November. 

December 

Annual. 

No.  2,  W.,  160 

feet . 

No.  3,  E.,  160 
feet . 

48.4 

48.8 

47.2 

47.4 

53.6 

53.7 

67.2 

66.8 

78.1 

77.4 

83.3 

82.4 

85.2 

84.8 

82.4 

82.3 

77.1 

77.0 

68.  8 

68.4 

58.2 

58.2 

45.5 

46.2 

66.3 

66. 1 

© 

1 

-0.2 

-0.1 

+0.4 

+0.7 

+0.9 

+0.4 

+0.1 

+0.1 

+0.4 

0. 0-0.7 

+0.2 

Plus  (+)  sign  excess  and  minus  (— )  sign  deficiency  of  No.  2  as  compared  with  No.  3. 


From  a  study  of  this  table  it  is  evident  that  the  seasonal 
variation  in  maximum  temperature  between  Nos.  2  and  3 
is  due  almost  wholly  to  the  varying  angle  of  the  sun’s 
rays  from  month  to  month  as  they  fall  upon  slopes  of 
different  direction  and  grade.  Beginning  with  April  and 
continuing  through  the  summer  and  into  the  fall,  No.  2 
is  warmer  because  at  the  time  of  maximum  temperature 
the  sun’s  rays  are  more  effective  at  that  station  than  at 
No.  3  on  the  east  slope,  as  brought  out  by  the  topographi¬ 
cal  map  (see  fig.  39).  In  the  winter  the  rays  of  the  sun, 
although  coming  from  a  lower  altitude,  fall  upon  No.  3 
almost  perpendicular,  because  at  that  location  the  ground 
slopes  downward  to  the  south  as  well  as  to  the  east, 
while  at  No.  2  the  slope  is  distinctly  westward,  the 
insolation  therefore  reaching  the  station  from  the  side. 
This  seasonal  variation  is  more  strongly  shown  in  Table 
la,  a  discussion  of  which  is  given  in  the  following 
paragraphs. 

During  the  sunshiny  period  in  May,  1914  (Table  la), 
No.  2  on  the  west  slope  averages  exactly  the  same  as  the 
base,  while  the  station  on  the  east  slope  at  the  same 
elevation,  160  feet  above  the  base,  averages  1.9°  lower 
than  the  base,  conforming  generally  to  the  theory  that, 
during  sunshiny  weather  a  west  exposure  has  a  higher 
day  temperature  than  an  easterly  slope.  The  summit, 
station,  200  feet  above  No.  3,  has  also  a  higher  tempera¬ 
ture  than  this  easterly  slope  station  during  the  period. 

The  variation  in  maximum  temperature  during  the 
clear  period  in  November  (Table  la)  is  much  the  same 
as  in  May,  with  the  exception  of  No.  2  on  the  west  slope, 
which  averages  2.3°  lower  than  No.  1,  while  there  is  no 
difference  between  these  two  stations  in  the  spring. 
Here,  again,  it  is  a  question  of  insolation,  the  sun  being 
low  in  the  south  in  November  and  its  rays  striking  No.  2 
from  the  side  with  small  heating  effect  as  compared  with 
their  influence  on  the  level  surface  at  No.  1 .  The  seasonal 
variation  between  Nos.  2  and  3  is  well  shown  in  this  table 
for  the  reasons  advanced  in  a  preceding  paragraph,  No.  2 
averaging  1.9°  higher  than  No.  3  in  May  and  0.4°  lower 
in  November.  Because  of  the  varying  effect  of  insolation 
at  No.  1  and  No.  4,  there  is  a  variation  of  0.7°  between 
the  average  differences  for  the  two  periods,  No.  4  being 
the  lower,  as  would  be  expected,  in  both  cases. 

Transon  (Table  1). — There  is  no  regularity  in  the  re¬ 
lation  between  the  maxima  at  the  Transon  stations. 
No.  2  on  the  west  slope,  150  feet  above  the  base,  averages 
2.1°  lower,  or  about  1°  for  71  feet  difference  in  elevation; 
yet  at  No.  3,  150  feet  higher  up,  the  average  maximum  is 
actually  0.2°  higher  than  at  No.  2.  On  the  other  hand, 


32 


SUPPLEMENT  NO.  19. 


No.  4,  on  the  summit,  with  an  elevation  of  450  feet  above 
the  base,  averages  3.5°  lower  than  the  base.  Either  the 
readings  at  Nos.  1  and  3  must  be  rather  high  or  those  at 
Nos.  2  and  4  rather  low  for  their  elevation.  As  a  matter 
of  fact,  both  of  these  conditions  may  be  true.  No.  1  is 
in  a  cove,  the  country  to  the  east  and  to  the  west  being 
rather  flat  for  a  mountainous  section  and  with  con¬ 
siderable  vegetation  around  the  shelter,  while  No.  3  has 
a  free  exposure  toward  the  west,  with  ample  sunshine. 
But  even  here  the  decrease  from  the  base  station  up  the 
slope  is  considerable,  1.9°  for  300  feet.  So  it  must  be 
considered  that  the  base  station,  at  least,  has  relatively 
high  maxima.  No.  4,  of  course,  has  a  free  exposure  on 
the  summit  of  a  small  knob  wdth  but  little  vegetal  cover, 
and  therefore  its  maximum  temperatures  are  lower  than 
No.  1,  especially  on  clear  days,  assuming,  of  course,  that 
the  sunshine  at  the  base  station  is  not  cut  off  materially. 
On  some  days  the  maxima  at  No.  4  are  actually  8°  lower 
than  at  No.  1.  During  November,  1914,  the  average 
difference  for  21  clear  days  was  4°,  with  an  extreme 
difference  of  8°,  while  during  a  period  of  clear  days  in 
May,  1914,  the  average  difference  was  3.6°,  with  an 
extreme  difference  of  6°.  On  cloudy  days  the  differences 
ranged  from  0.6°  to  2.3°. 

In  a  comparison  of  the  maxima  during  the  May  period 
of  clear  weather  (Table  la)  the  relations  between  sta¬ 
tions  Nos.  1,  2,  and  4  seem  to  be  about  the  same  as  shown 
by  the  four-year  averages,  the  differences  at  these  sta¬ 
tions,  as  stated  above,  being  rather  large  considering  the 
slight  elevations.  Station  No.  3,  however,  on  the  west 
slope,  has  a  relatively  high  maximum  during  the  period 
of  sunshine,  as  should  be  expected. 

The  variation  during  the  clear  period  in  November  is 
somewhat  different  from  that  in  May,  in  that  station 
No.  3  averages  considerably  lower  than  the  base,  the 
difference  being  2.5°,  while  in  May  there  is  a  decrease  of 
but  0.4°.  However,  as  in  the  spring  period,  the  averages 
at  all  the  upper  stations,  Nos.  2,  3,  and  4,  are  lower  than 
at  the  base. 

Tryon  (Table  1). — The  decrease  in  maximum  temper¬ 
ature  from  the  base  station,  No.  1,  to  Nos.  2,  3,  and  4  is 
not  uniform  but  most  irregular.  The  slight  average 
difference,  only  0.5°  between  Nos.  1  and  2  for  a  difference 
in  height  of  380  feet,  can  be  accounted  for  by  the  large 
amount  of  vegetation  at  No.  2,  this  causing  a  relatively 
high  maximum  at  that  point.  Moreover,  No.  2  is  on  a 
rather  flat  surface  on  a  general  southeasterly  slope,  so 
that  the  maximum  there  approximates  closely  that  at 
No.  1  in  the  valley.  In  fact  on  sunshiny  days  the 
temperature  at  No.  2  is  as  high  or  higher  than  that  at 
No.  1,  while  on  cloudy  days  it  is  often  a  degree  or  more 
lower. 

The  average  maximum  at  station  No.  3,  570  feet  above 
the  base,  is  abnormally  low,  the  average  decrease  being 
3.1°,  equivalent  to  1°  for  184  feet.  There  is,  moreover, 
an  average  decrease  of  2.6°  from  No.  2  to  No.  3,  although 
the  difference  in  elevation  is  only  190  feet,  amounting 
to  1°  for  73  feet.  The  No.  2  shelter  is  located  just  below 
the  lower  edge  of  a  vineyard  in  a  plot  of  long  grass  and 
weeds,  while  No.  3  is  directly  above  the  upper  edge  in  a 
small  orchard  where  vegetation  is  rather  thin.  We 
should  expect  more  than  the  usual  decrease  between 
Nos.  2  and  3,  because  No.  2  is  the  more  favorably  situated 
for  high  day  temperatures  during  periods  of  sunshine; 
but  the  unusual  difference  of  2.6°  on  an  average  seems 
rather  difficult  to  explain. 

The  apparent  discrepancy  might  be  accounted  for 
possibly  by  assuming  that  the  thermometer  at  No.  3 
registered  1°  too  low,  but  this  supposition  is  hardly 


justified,  because  of  the  close  attention  given  to  the 
instruments. 

In  connection  with  the  above,  it  is  interesting  to  note 
that  the  maximum  at  the  summit  station  in  its  relation 
to  the  base,  1,100  feet  below,  appears  to  be  normal,  as 
there  is  a  decrease  between  the  two  of  3.8°,  or  1°  for  289 
feet.  This  fact  makes  the  maximum  readings  at  station 
No.  3  appear  even  more  strange,  that  station  averaging 
only  0.7°  higher  than  No.  4,  although  the  difference  in 
elevation  between  Nos.  3  and  4  is  530  feet.  In  fact,  No.  4 
conforms  so  closely  to  what  should  be  expected  for  all  the 
months  of  the  year  that  the  record  at  that  point  does  not 
require  detailed  discussion. 

The  comparison  of  the  selected  sunshiny  periods 
(Table  la)  does  not  explain  the  apparent  anomaly  at 
station  No.  3.  The  average  of  the  maxima  at  No.  2 
during  the  period  of  clear  weather  in  May  is  1.5°  higher 
than  the  base  station,  but  the  average  at  No.  3  is  4.1° 
lower.  In  the  selected  May  period  No.  4  has  a  com¬ 
paratively  low  maximum,  being  6°  lower  than  the  base. 

In  the  November  clear  period  (Table  la),  the  varia¬ 
tion  is  more  regular,  as  there  is  a  gradual  decrease  from 
the  base  to  the  summit,  the  difference  being  relatively 
great  between  stations  Nos.  2  and  3,  but  not  nearly  so 
great  as  during  the  May  period. 

WiTkesboro  (Table  1). — Station  No.  1  is  located  in  a 
comparatively  flat  open  plot  on  a  bench  although  not  so 
extensive  as  that  at  Mount  Airy,  but  sufRcienctly  so  to 
cause  relatively  high  maximum  temperatures.  More¬ 
over,  No.  2,  150  feet,  and  No.  3,  350  feet,  above  the  base, 
are  located  on  northerly  slopes,  and  therefore  their 
maxima  are  relatively  low.  No.  4  also  has  a  rather 
low  maximum,  with  a  decrease  of  2.4°  for  an  elevation 
of  430  feet  above  the  base.  The  markedly  super- 
adiabatic  rate  of  decrease  in  temperature  is  undoubtedly 
due  to  the  character  of  the  exposure  of  No.  1,  which  is 
unduly  heated  on  sunshiny  days  during  the  entire  year; 
but  the  more  direct  insolation  and  the  retarded  air 
movement  over  the  flat  surface,  with  the  increased 
vegetation  during  the  warmer  months  of  the  year, 
produce  relatively  higher  maximum  temperatures  than 
in  the  autumn,  when  the  effect  of  vegetation  is  practically 
at  a  minimum.  Nos.  2,  3,  and  4  are  ideal  slope  stations 
with  open  exposure,  which  in  itself  would  be  sufficient 
reason  for  the  relatively  low  maximum  temperatures 
at  these  locations  as  compared  with  No.  1  in  all  months 
of  the  year. 

During  both  sunshiny  periods,  as  shown  by  Table  la, 
the  decrease  is  much  greater  at  Wilkesboro  than  the 
four-year  averages  would  indicate.  Considering  the 
shortness  of  the  slope,  the  decrease  in  maximum  tempera¬ 
ture  is  greater  here  than  at  any  other  place,  there  being 
a  decrease  of  3.9°  for  a  difference  in  elevation  of  430  feet 
between  No.  1  and  No.  4. 

Variations  in  maximum  temperature  in  clear  and  cloudy 
weather. — The  irregularities  in  clear  weather  are  due 
largely  to  local  exposure  in  the  shape  of  timber  and 
topography,  which  cut  off  the  sunshine  in  varying 
degrees  near  the  time  of  maximum  temperature,  and  to 
surrounding  vegetation,  which  allows  abnormal  local 
heating  of  the  air.  There  are  a  number  of  instances  of 
this  abnormal  heating,  especially  at  Highlands  No.  2, 
Asheville  No.  3a,  Blantyre  No.  4,  Bryson  No.  3,  Cane 
River  No.  4,  Globe  No.  3,  Transon  No.  1,  and  Tryon  No. 
2,  as  brought  out  under  the  discussion  of  maximum 
temperature  on  the  individual  slopes.  Generally  speak¬ 
ing,  this  factor  is  most  important  during  the  growing 
season,  probably  most  effective  from  May  to  August, 
when  vegetation  is  densest,  and  least  effective  during  the 


33 


THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 


winter.  However,  the  conditions  noted  during  the 
selected  period  in  May  (Table  la)  are  dependent  on  sun¬ 
shine  at  the  time  of  the  maximum  temperature,  but  the 
frequent  cloudiness  in  the  afternoon  at  the  time  of  the 
maximum  temperature  during  June,  July,  August,  and 
September  minimizes  local  overheating  at  these  stations, 
so  that  the  decrease  in  maximum  temperature  does  not 
differ  greatly  from  the  normal  decrease  with  elevation. 

With  the  approach  of  clear  weather  in  autumn,  the 
maximum  temperature  at  such  stations  is  again  slightly 
increased,  although  the  decrease  in  the  surrounding 
vegetation  prevents  the  marked  local  heating  which 
occurs  in  April  and  May.  However,  it  will  be  noted  that 
the  four-year  average  excess  in  maximum  temperature 
for  November,  as  shown  in  Table  1,  at  the  summit 
stations,  Asheville  No.  3a  and  Blantyre  No.  4,  over  those 
at  the  bases  is  about  equal  to  the  excess  recorded  in  the 
spring,  but  this  is  not  due  entirely  to  the  increase  in  the 
percentage  of  sunshine,  as  is  the  case  at  the  remaining 
stations,  but  rather  to  other  reasons  which  have  been 
described  previously. 


Fig.  45. — Average  daily  maxima  during  selected  period  of  clear  weather  in  spring; 
stations  grouped  according  to  elevation  above  sea  level. 


Naturally,  there  is  greater  uniformity  in  the  decrease 
in  temperature  with  elevation  during  cloudy  weather 
than  during  days  of  sunshine,  as  then  the  effect  of  local 
overheating  is  avoided. 

The  figures  in  Table  lb  show  the  rate  of  the  decrease  on 
selected  days  of  cloudy  weather  in  the  year  1915  on  the 
three  long  slopes  having  five  stations  from  base  to  summit, 
separated  from  each  other  more  or  less  uniformly. 

The  rates  of  decrease  in  temperature  on  these  three 
slopes  are  fairly  uniform  at  different  elevations,  and  for 
the  slopes  as  a  whole  there  is  a  decrease  of  1°  for  each 
312  feet  at  Altapass,  each  326  feet  at  Ellijay,  and  each 
347  feet  at  Gorge.  These  rates  are  all  less  than  the 
normal  rate  of  decrease  in  free  air — 1°  for  300  feet 
doubtless  because  of  the  higher  vapor  pressuie  under 

cloudy  conditions.  ,  .  , 

Figures  45  and  46  furnish  a  grapmc  representation  ot 
the  variation  in  maximum  temperature  at  all  the  stations 
in  the  research  during  the  selected  clear  periods  in  spung 

and  autumn.  .  . 

The  high  maximum  at  Tryon  No.  2  in  autumn  (fig.  46) 
as  compared  with  the  others  at  the  same  elevation  is  due 
to  more  insolation  on  this  southeast  slope  and  is  in  con¬ 
trast  with  the  slight  differences  in  the  averages  during 
the  spring  period  (fig.  45).  There  is  also  here  apparent, 


for  the  same  reason,  a  marked  difference  between  the 
stations  Nos.  2  and  3  at  Mount  Airy  in  the  spring  as 
compared  with  the  readings  in  autumn,  doubtless  because 
the  direction  of  slope  is  not  so  important  in  the  spring. 

Other  instances  bearing  upon  this  point  will  be  found, 
such  as  the  readings  at  stations  Nos.  2  at  Globe  and 
No.  3  at  Gorge,  and  Asheville  stations  Nos.  3  and  3a. 
Cane  River  No.  3,  located  in  a  cove  on  a  northerly  slope, 
is  also  another  striking  example  of  difference  in  insolation 
between  spring  and  autumn.  Then  there  are  the  rela¬ 
tively  high  readings  in  the  spring  at  Bryson  No.  3  and 
Cane  River  No.  4,  both  summit  stations,  due  to  the 
large  amount  of  vegetation  which  traps  and  radiates  the 
heated  air  near  the  shelters. 

Rates  of  decrease  in  monthly  and  annual  average  maxi¬ 
mum  temperature  on  six  selected  long  slopes. — -The  figures 
in  Table  lc  show  that  for  the  entire  period  of  four  years 
the  rate  of  decrease  in  average  maximum  temperature 
with  elevation  on  the  Altapass,  Ellijay,  and  Gorge  slopes 
was  greater  than  during  the  cloudy  period  included  in 
Table  lb. 


Fig.  46. — Average  daily  maxima  during  selected  period  of  clear  weather  in  autumn; 
stations  grouped  according  to  elevation  above  sea  level. 


The  largest  decrease  is  found  at  Altapass,  with  a  rate 
of  1°  for  each  238  feet.  Ellijay  is  close  to  the  normal 
rate  for  free  air,  with  1°  for  each  303  feet,  and  Gorge 
less  than  the  normal,  with  1°  for  each  325  feet. 

The  data  are  included  in  Table  lc  also  for  the  three 
other  long  slopes,  Cane  River,  Globe,  and  Tryon. 

The  rates  of  decrease  at  Cane  River  and  Globe,  1°  for 
each  423  feet  and  455  feet,  respectively,  are  abnormal 
because  of  local  conditions  previously  referred  to,  while 
the  rate  at  Tryon  is  about  normal,  with  1°  for  each  289 

feet.  .  . 

Monthly  and  annual  average  maxima  at  the  two  stations 
having,  respectively ,  the  highest  and  lowest  elevations  .—A. 
comparison  is  made  in  Table  Id  for  the  four-year  period 
between  the  average  maximum  temporatures  at  the 
lowest  and  the  highest  stations  employed  in  the  research, 
Tryon  No.  1,  950  feet  in  elevation,  base  station,  and 
Highlands  No.  5,  4,075  feet  in  elevation,  the  summit 
station.  The  difference  in  elevation  between  these  two 
stations  is  3,125  feet,  the  extreme  range  employed  in 

this  research.  ... 

For  this  difference  in  elevation  there  is  an  average 
four-year  difference  in  maximum  temperature  of  1L5.  , 
the  greatest  average  monthly  difference  being  15.6  in 
Mar  oh  and  the  least  8.3°  in  December. 


34 


SUPPLEMENT  NO.  19. 


The  rate  of  decrease  for  the  entire  period  between 
these  two  stations  is  1°  for  272  feet.  The  difference  in 
latitude  between  Tryon  and  Highlands  is  negligible 
in  so  far  as  its  effects  on  temperature  are  concerned, 
both  being  located  close  to  the  southern  boundary  of 
the  State. 

MINIMUM  TEMPERATURE. 

Inversions  and  norms. — The  subject  of  minimum 
temperature  in  mountain  sections  is  much  more  compli¬ 
cated  than  that  of  maximum.  There  is  usually  a  certain 
uniformity  in  the  variation  of  mean  maximum  tempera¬ 
ture,  because  on  most  slopes  there  is  an  average  decrease 
from  the  lowest  to  the  highest  elevations;  but  no  such 
regular  decrease  is  found  in  the  averages  of  minimum 
temperature.  This  is  because  on  some  nights  there  is  a 
steady  decrease  in  temperature  from  the  base  to  the 
summit,  on  other  nights  an  increase,  and  on  still  other 
nights  an  increase  to  a  certain  point  on  the  slope  and  then 
a  decrease  farther  up.  So,  in  the  one  instance  we  have 
the  usual  decrease  in  temperature  on  account  of  eleva-  ' 
tion,  called  here  “norm”  for  the  sake  of  convenience, 
and  in  the  other  two,  the  variations  due  to  both  inversion 
and  norm  conditions.  There  is  usually  a  decrease  in 
minimum  temperature  from  the  base  to  the  summit 
on  cloudy  or  windy  nights,  while  on  comparatively  clear 
nights,  with  little  or  no  wind,  an  inversion  occurs  with 
the  lowest  temperature  in  every  case  at  the  base.  Some¬ 
times,  there  is  even  a  combination  of  the  two,  norm  and 
inversion,  as  we  shall  point  out  later. 

Additional  types  of  inversions. — When  reference  is  I 
made  in  meteorological  literature  to  night  inversions,  it  I 
has  been  generally  understood  that  they  occur  only  in  a  | 
region  with  high  pressure,  clear  weather,  and  light  wind 
or  calm.  It  is  seldom  stated  that  inversions  of  con¬ 
sequence  occur  under  other  conditions,  but  this  study  in 
the  Carolina  mountain  region  furnishes  additional  in¬ 
formation  on  the  subject.  True  it  is  that  the  most 
marked  instances  of  inversion  usually  occur  under  high- 
pressure  conditions,  but  we  find  that  inversions  obtain 
also  in  the  passing  of  the  high  tlnd  in  the  approach  of 
the  low.  We  have  in  consequence  concluded  that  in¬ 
versions  may  be  divided  into  three  different  types,  the 
Anticyclonic  or  Ideal  Type,  the  Recovery  or  Inter¬ 
mediate  Type,  and  the  Cyclonic  or  Overflow  Type. 

The  Anticyclonic  or  Ideal  Type  is  of  course  the  one 
best  known,  and  the  best  examples  of  this  type  occur 
when  the  anticyclone  persists  two  or  more  days. 

The  Recovery  or  Intermediate  Type  is  marked  by  a 
more  rapid  movement  of  anticyclones  than  in  the  first- 
named  type,  and  occurs  during  the  transition  from  an 
anticyclone  to  a  cyclone.  Inversions  of  this  character 
are  pronounced  on  only  one  night,  as  a  rule,  but  they  are 
sometimes  greater  than  those  found  under  the  Anti¬ 
cyclonic  Type.  The  Recovery  Type  is  usually  accom¬ 
panied  by  clear  weather  and  light  winds  and  is  largely 
due  to  the  stagnation  of  the  colder  and  heavier  air  with 
a  further  fall  in  temperature  in  the  hollows  and  pockets, 
where  the  lower  stations  are  located,  while  the  warmer 
and  lighter  air  above,  as  it  is  drawn  into  an  approaching 
cyclone,  flows  over  the  summits  and  the  upper  slopes. 

The  Cyclonic  or  Overflow  Type  is  characterized  by 
moderate  to  strong  winds  and  rapidly  falling  pressure, 
with  a  well-developed  cyclone  approaching.  During 
inversions  of  this  type  the  low  temperatures  at  the  base 
stations  are  due  to  the  confinement  of  air,  already  cold, 
in  the  pockets  and  narrow  valleys,  while  the  strong 
southerly  winds,  which  usually  prevail  in  the  North 
Carolina  region,  bring  warm  air  to  the  higher  stations, 


and  although  these  winds  soon  draw  the  colder  air  out 
of  the  pockets,  sometimes  this  does  not  occur  in  time  to 
prevent  a  strong  inversion.  The  Cyclonic  Type  occurs 
most  frequently  in  the  winter  months,  when  there  is 
pronounced  storm  activity. 

Each  one  of  the  three  types  often  merges  into  one  of 
the  two  others,  so  that  many  of  the  weaker  inversions 
may  be  placed  in  any  two  of  the  three  types.  There  is 
often  no  sharp  line  of  demarcation  between  the  Inter¬ 
mediate  Type  and  the  Cyclonic  Type,  and  yet  at  other 
times  these  two  classes  have  their  individual  and  distinct 
characteristics. 

Anticyclones  occasionally  dominate  the  weather  in  the 
Carolina  mountain  region  for  a  week  or  more  at  a  time, 
and  it  is  then  that  pronounced  inversions  of  the  Ideal 
Type  occur.  No  month  is  without  inversions,  and  rarely 
a  week  goes  by  without  one  of  considerable  range.  They 
are  most  frequent  and  reach  their  greatest  development 
during  the  spring  and  autumn,  with  maxima  in  May  and 
November.  In  these  two  seasons  the  inversions  belong 
almost  entirely  to  the  Anticyclonic  or  Ideal  Type,  with 
rarely  an  inversion  of  the  Cyclonic  Type. 

Mountain  breezes.3 — So  far  in  the  discussion  of  inver¬ 
sions  no  reference  has  been  made  to  certain  complications 
in  valleys  caused  by  the  direct  flow  of  air  downward  from 
above — a  subject  of  considerable  moment. 

When  the  air  resting  fibove  a  slope  becomes  cold  com¬ 
pared  with  the  free  air  over  the  valley  floor,  it  descends 
the  slope  in  the  form  of  a  night  wind  or  breeze,  common 
in  mountain  sections,  and  as  such  a  breeze  is  not  gradual 
but  sudden  the  air  in  descending  is  heated  mechanically. 
This  condition  is  graphically  shown  by  thermograph 
traces  of  temperatures  on  the  slope  at  Asheville  No.  2 
and  on  the  valley  floor  at  Tryon  No.  1,  the  temperature 
rising  as  the  rush  of  air  passes  the  instrument  (see  figs. 
56  and  63).  It  may  be  said  that  in  the  convective  inter¬ 
change  the  flow  is  nonwaterlike,  but  when  air  descends 
the  slope  in  a  mountain  breeze  it  is  a  waterlike  flow.  In 
the  inclosed  valleys  or  basins  such  a  flow  is  never  ob¬ 
served,  but  in  valleys  having  an  outlet,  especially  those 
adjoining  deep  canyons  that  afford  good  opportunities  for 
drainage  and  where  the  extent  of  surface  area  aloft  is 
great,  it  is  noted  frequently. 

An  example  of  a  sudden  rise  in  night  temperatures 
at  a  slope  station  due  to  the  replacement  of  unusually 
cold  air  by  the  warmer  free  air  adjoining  is  shown  by  the 
thermograph  curve  at  Asheville  No.  2,  Figure  55,  and 
at  Blantyre  No.  2,  Figure  56;  and  an  example  of  a  rise 
on  the  valley  floor  caused  by  the  downrush  of  air  from 
the  mountain  above,  as  often  experienced  at  Tryon,  is 
illustrated  in  Figure  62.  These  figures  will  be  discussed 
later. 

Average  monthly  and  annual  minimum  temperature. — 
Table  2,  average  minimum  temperatures  and  differences, 
1913  to  1916,  monthly  and  annual,  presents  the  data 
much  the  same  as  does  Table  1  for  the  maximum,  and 
Table  2a  presents  data  for  inversion  and  norm  periods 
just  as  Table  la  includes  data  for  periods  of  clear  weather 
in  connection  with  maximum  temperature  values.  There 
is,  as  has  been  stated  before,  a  much  greater  variation 
in  the  minimum  than  in  the  maximum  temperature,  and 
we  shall  note  also  a  much  wider  variation  during  inver¬ 
sion  than  during  norm  conditions. 

r  Two  periods,  May  1-6,  1913,  and  November  2-5,  1916 
(Table  2a),  have  been  selected  as  typical  of  clear  weather 
in  which  marked  inversions  of  temperature  are  noted, 
the  one  with  gentle  to  light  southerly  winds  and  the 

3  The  author  is  here  dealing  with  the  nighttime  feature  of  the  well-known  phenomenon 
of  mountain  and  valley  winds. — Editor. 


THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 


35 


other  with  northerly  winds,  periods  with  different  wind 
directions  being  selected,  as  the  direction  is  an  important 
factor  in  affecting  minimum  temperature  on  nights  of 
inversion. 


The  two  periods  are  probably  as  representative  as 
any  that  might  be  selected,  permitting,  as  they  do,  the 
discussion  of  the  question  of  inversion  as  far  as  may  seem 
necessary  at  this  time  in  connection  with  the  chapter  on 
average  minimum  temperature.  Later  the  subject  of 
inversion  will  be  treated  separately  and  in  greater 
detail. 

It  is  rather  difficult  to  find  a  period  of  several  days  m 
succession  in  which  norms  occur  on  all  the  slopes  under 


investigation;  and  the  dates  selected  in  1916,  eight  in  all, 
and  included  in  Table  2a,  are  not  consecutive,  but  they 
will  serve  to  illustrate  the  variation  in  minimum  tem¬ 
perature  during  these  special  conditions. 


The  data  for  both  inversion  and  norm  periods  as  shown 
by  Table  2a  should  be  helpful  in  explaining  the  variations 
in  average  minimum  temperature  on  the  various  slopes. 
A  discussion  now  follows  embracing  Tables  2,  2a,  2b, 
and  Figs.  47,  48,  and  49,  which  present  data  for  the 
various  groups  of  stations. 

The  average  minima  to  be  discussed  here  will  be  limited 
to  night  readings,  just  as  the  average  maxima  have  been 
limited  to  day  readings. 


Table  2. — Monthly  and  annual  average  minimum  temperatures,  1913-1916. 


[The  differences  between  the  averages  at  the  base  station  and  those  of  the  respective  slope  stations  may  be  seen  by  simple  inspection.] 


Principal  and  slope  stations; 
elevation  of  base  station  above 
mean  sea  level  (feet). 

Height 
of  slope 
station 
above 
base 
(feet). 

Altapass: 

No.  1,  base  station,  elevation 

9  9sn  . 

Nn'  9  RF,  . 

250 

No.  3^  SE . 

500 

750 

1,000 

Asheville: 

No.  1,  base  station,  eleva- 

No.  2,  N . 

No  2a  S  . 

155 

155 

No  3  N  . 

380 

380 

Blantyre: 

No.  1,  base  station,  eleva- 

300 

No  3  NW  . 

450 

600 

Blowing  Rock: 

No.  1,  base  station,  eleva- 

No.  2,  SW . 

No  3  SE  . 

450 

450 

No  4  SE  . 

625 

No  ft  SE  . 

800 

Bryson: 

No.  1,  base  station,  eleva- 

Nn  2  N  . 

385 

No  2a,  S . 

385 

No.  3,  summit . 

570 

Janu¬ 

ary. 

Febru¬ 

ary. 

March. 

April. 

131.1 

1  29.1 

1  31.5 

144.2 

1  31.5 

1  29.6 

1  31.3 

1  45.3 

1  31.4 

1  29.3 

1  30.8 

1  44.5 

1  29.4 

1  27.3 

1  28.9 

1  42.3 

1  29.1 

1  27.0 

1  28.8 

1  42.1 

32.3 

28.8 

32.9 

41.8 

33.3 

29.7 

33.6 

43.6 

34.  5 

30.6 

34.7 

45.0 

33.9 

30. 1 

34.1 

44.7 

34.5 

30.4 

34.4 

45. 4 

30.1 

26.6 

30.2 

38.4 

31.4 

27.8 

32.2 

41.6 

32.5 

29.2 

32.8 

43.7 

33.5 

30.6 

33.8 

45. 0 

30.0 

26.6 

30.2 

41.2 

30.0 

26.4 

29.9 

42.4 

27.2 

23.4 

27.6 

37.1 

29.0 

25.3 

29.0 

40.5 

28.0 

24.6 

28.0 

39.6 

2  31.3 

’  >27.4 

1  28.3 

39.4 

2  32.6 

1  28.  6 

1  29.5 

41.3 

2  33.  1 

1  29.0 

1  29.8 

42.4 

2  33.8 

129.9 

130.8 

44.4 

i  Three-year  average. 


May. 

June. 

July. 

August. 

Septem¬ 

ber. 

October. 

Novem¬ 

ber. 

Decem¬ 

ber. 

Annual. 

52. 8 

58.4 

62.5 

61.3 

54.0 

46.3 

36.6 

29.8 

1  44.8 

54  0 

59. 2 

63.1 

62.1 

55.5 

48.2 

38.4 

30.  2 

1  45.  7 

53.6 

58.6 

62.7 

62.0 

55.3 

48.0 

37.9 

29.7 

1  45. 3 

51.  8 

56.  7 

60.5 

60.1 

53.3 

46.6 

36.2 

27.8 

1 43. 4 

51.0 

55.8 

60.2 

59.5 

52.5 

45.2 

35.4 

27.4 

1 42. 9 

50  7 

56.6 

60.3 

59.8 

52.6 

44.6 

34.4 

28.8 

43.6 

59  9 

58.  0 

61.4 

60.4 

54.6 

45.  9 

36.5 

29.  5 

45.  0 

53  9 

59. 1 

62.4 

61.7 

55.7 

47.5 

37.6 

30.9 

46. 1 

54  9 

60.0 

63.2 

62.3 

55. 6 

47.9 

38.8 

30.8 

46. 4 

55.2 

60.1 

63.4 

62.6 

56.3 

48.4 

38.8 

30.  8 

46.  7 

47  7 

56. 1 

60.7 

60.6 

52.8 

43.2 

29.7 

26.0 

41,8 

49.6 

52.1 

54.0 

56.0 

57.2 

58.4 

59.8 

61.2 

62.5 

59.6 

60.6 
61.8 

51.7 

53.4 

55.3 

43.0 
45. 3 
47.0 

31.8 

35.5 

37.5 

27.3 
29.1 

30.3 

42.  6 
44.4 
45.8 

50.2 

51.9 

46.1 

50.2 
49.8 

56.9 

57.2 

53.3 

55.9 
55.6 

60.6 

60.9 

56.8 

59.9 
59.2 

60.4 

60.4 
56.3 
59.0 

58.5 

53.6 
53.8 

48.4 

52.4 

51.6 

45.4 

45.8 
42.2 
44.6 

43.8 

35.0 

36.8 
29.6 
35.0 

33.8 

27.2 
27.6 
24.0 

26.2 
25.2 

43.1 
43.6 

39.3 

42.2 

41.4 

48.  5 
49.7 
50.6 
52.3 

55.7 
56.0 

56.8 
57.6 

60.0 
59.  8 
61.2 
61.2 

59.8 

59.6 

60.6 

60.8 

52.6 
53.0 
53.3 

53.6 

43.1 

44.2 
44. 1 
46.0 

130.7 

133.6 

133.7 

1  36.2 

1  26.5 
127.9 

1  28.2 

1  29.0 

1  41.9 
1  43.0 
143.6 
1  44.6 

•Two-year  average. 


36 


SUPPLEMENT  NO.  19. 

Table  2. — Monthly  and  annual  average  minimum  temperatures,  1913-1916 — Continued. 

[The  differences  between  the  averages  at  the  base  station  and  those  of  the  respective  slope  stations  may  be  seen  by  simple  inspection.] 


Principal  and  slope  stations : 
elevation  of  base  station  above 
mean  sea  level  (feet). 

Height 
of  slope 
station 
above 
base 
(feet). 

Janu¬ 

ary. 

Febru¬ 

ary. 

March. 

April. 

May. 

June. 

July. 

August 

Septem¬ 

ber. 

October. 

Novem¬ 

ber. 

Decem¬ 

ber. 

Annual. 

Cane  River: 

No.  1,  base  station,  eleva- 

1  26.4 

125.7 

1  27.2 

37.6 

46.6 

53.9 

58.1 

58.0 

49.6 

40.4 

28.5 

33.7 

35.2 

36.3 

24.8 

27.6 

27.3 

27.2 

39.7 

42.1 

142.6 

142.8 

No.  2,  N . 

190 

1  29.9 

1  27.2 

1  28.9 

40.9 

49.6 

55.4 

59.1 

58.7 

51. 3 

43.0 

No.  3'  NE  . 

400 

1  29.5 

126.1 

1  27.9 

41.3 

51.0 

56.2 

59.8 

59. 4 

52. 5 

44.4 

1,100 

1  28.8 

1  26.9 

1  27.1 

41.0 

51.3 

56.7 

60.2 

59.6 

53. 1 

45. 3 

Ellijay: 

No.  1,  base  station,  eleva- 

130.2 

127.7 

128.6 

39.7 

48.2 

54.7 

58.8 

58.4 

51.1 

42.5 

31.1 

27.4 

28.6 

29.7 

31.1 

1  28.6 

2  41.6 

2  43.7 

2  44.4 

2  45.8 

1  44.9 

No.  2,  . 

310 

131.1 

130.0 

130.5 

42.6 

51.0 

56.6 

59.9 

59.0 

52.0 

43.  7 

33.  8 
36.7 

No.  3’  N  . 

620 

1  31.9 

129.9 

130.5 

43.2 

52.2 

57.1 

60.4 

59.6 

53.3 

45. 3 

1,240 

132.8 

1  30.8 

>30.8 

45.4 

54.8 

59.4 

62.1 

61.2 

55. 3 

47.7 

39. 1 

1,760 

232.6 

2  29.6 

1  28.6 

1  44.2 

1  54.0 

158.4 

160.9 

160.0 

1 54.7 

1  48. 1 

1  37.7 

Globe: 

No.  1,  base  station,  eleva- 

31.8 

29.0 

32.4 

41.9 

51.1 

58.0 

62.0 

61.6 

54.6 

46.5 

34.6 

29.2 

31.2 

44.4 

No.  2,  E . 

300 

33.4 

30.6 

34.3 

45.1 

55.0 

60.5 

64. 1 

63.5 

57.0 

49.3 

38.6 

46.  9 
47.2 

1,000 

33.6 

30.4 

33.8 

46.0 

55.9 

61.2 

64.6 

63.5 

57.2 

49.7 

39.8 

30.8 

Gorge: 

No.  1,  base  station,  elevation 

1  400  . 

30.8 

28.1 

32.3 

40.5 

49.3 

56.8 

61.1 

61.0 

53.9 

45.2 

32.8 

27.9 

43.3 

Nn  2  NE . 

290 

30.6 

27.8 

32.0 

41.2 

50.2 

57.2 

61.0 

60.8 

53.6 

45.1 

33.8 

28.6 

43-  5 

No.  3, 7  S . 

615 

32.4 

29.6 

33.6 

43.8 

52.3 

58.0 

61.8 

61.0 

54.2 

45.8 

36.6 

29.7 

44.9 

No.  4,  N.  (old);  NE.  (new).. 

840 

1,040 

33.0 

33.5 

30.2 

30.9 

34.4 

34.4 

45.6 

46.9 

54.8 

57.0 

59.7 

61.4 

63.2 

64.9 

62.4 

63.7 

55.9 

57.7 

48.0 

49.9 

39.1 

41.1 

30.6 

32.0 

46.  4 
47.8 

Hendersonville: 

No.  1,  base  station,  eleva- 

1  28.9 

1  27.3 

1  28.3 

38.8 

47.8 

55.4 

59.6 

59.8 

51.8 

43.2 

31.1 

27.4 

42.0 

No  2,  IS . 

450 

1  30.7 

1  28.5 

1  30.3 

41.7 

50.8 

57.7 

61.1 

60.5 

53.0 

44.9 

34.4 

28-9 

44.7 

No  3,7  E  . 

600 

1  31.5 

129.8 

130.7 

44.0 

53.2 

58.7 

61.8 

61.4 

54.7 

46.9 

37.4 

29.7 

46.2 

750 

131.7 

1300 

1309 

44.6 

54.2 

59.3 

62.6 

61.6 

55.5 

47.8 

38.4 

30.1 

46.8 

Highlands: 

No.  1,  base  station,  eleva- 

132.2 

1  28.9 

130.4 

44.2 

53.2 

58.3 

61.6 

61.0 

55.2 

47.0 

38.0 

30.7 

45  1 

No  2,  SE . 

200 

1  33.0 

131.1 

130.2 

44.2 

53.4 

58.5 

61.7 

61.4 

55.3 

47.4 

38.9 

31.8 

456 

No.  3’  SE . 

325 

1  26.8 

123.4 

1  24.4 

34.6 

43.4 

49.4 

53.5 

53.0 

45.7 

38.0 

27.7 

234 

37.0 

No  4,  SE . 

525 

1  29.0 

125.9 

126.0 

41.2 

50.7 

55.6 

58.5 

57.6 

51.3 

44.2 

35.8 

27.2 

41.8 

No  5 7  SE . 

725 

1  28.6 

125.7 

125.4 

41.5 

51.4 

56.5 

59.8 

58.7 

52.6 

46.0 

36.8 

28.6 

42.5 

Mount  Airy: 

No.  1,  base  station,  eleva- 

33.0 

30.0 

34.6 

45.0 

53.6 

60.5 

64.0 

63.4 

56.3 

48.2 

37.0 

302 

46.3 

No.  2,  W . 

160 

34.3 

314 

35.6 

47.2 

57.2 

63.1 

66.3 

64.7 

58.8 

51.3 

41.0 

32.2 

48.6 

No.  3,  E  . 

160 

34.0 

30.8 

35.3 

46.4 

55.6 

61.8 

64.7 

64.0 

57.6 

49.7 

39.0 

31.8 

47.6 

360 

33.9 

30.8 

34.7 

46.8 

56.8 

62.6 

66.0 

64.9 

58.8 

51.2 

40.6 

31.8 

48.2 

Transon: 

No.  1,  base  station,  eleva- 

28.8 

24.7 

28.4 

38.3 

46.4 

53.3 

57.6 

56.6 

48.8 

41.4 

30.4 

24.5 

40.0 

Nn  2  W  . 

150 

30.6 

26.4 

29.8 

41.4 

51.2 

56.7 

59. 8 

59.2 

52.0 

43.8 

34.9 

26.8 

42.8 

No.  %  W . 

300 

30.4 

26.8 

29.8 

41.8 

51.2 

57.2 

60.6 

59.8 

52.8 

45.1 

35.9 

27.0 

43.2 

450 

1  29. 1 

1  27.2 

127.8 

42.0 

52.3 

57.5 

60.8 

60.0 

54.2 

46.3 

36.9 

27.3 

43.8 

Tryon: 

’  No.  1,  base  station,  eleva- 

34.7 

32.3 

35.9 

44.7 

54.8 

63.0 

66.7 

66.3 

58.5 

50.6 

37.3 

32.8 

48.1 

No.  2,  SE . 

380 

38.1 

36.0 

39.4 

50.8 

60.4 

65.7 

69.0 

67.6 

61.  4 

.53.8 

44.3 

35.9 

51.8 

No.  37  SE . 

570 

37.6 

34.8 

38.1 

49.7 

58.8 

64.2 

67.5 

66.4 

59.9 

52.2 

43.0 

34.4 

50.5 

No.  4,  SE . 

1,100 

35.8 

33.3 

36.2 

47.5 

56. 9 

61.9 

65.0 

64.4 

58.0 

47.7 

40.6 

32.8 

48.8 

Wilkesboro: 

No.  1,  base  station,  eleva- 

31.6 

28.8 

33.8 

43.4 

52. 1 

59.2 

63.3 

62.8 

55.6 

46.4 

35.0 

29.0 

45.0 

No.  2,  N . 

150 

33.1 

30.4 

35.2 

45.7 

54.9 

60.6 

64.4 

63.7 

56.2 

48.4 

37.6 

30.7 

46.7 

No.  3,  N . 

350 

34.2 

31.8 

36.2 

47.5 

57.0 

62.3 

66.2 

65.0 

58.2 

50.6 

40.6 

32.2 

48.5 

No.  4,  W . 

430 

34.2 

31.4 

35.8 

47.4 

57.3 

62.6 

66.5 

65.6 

58.3 

50.6 

41.2 

32.3 

48.6 

I 

1  Three-year  average.  2  Two-year  average. 


Average  Minimum  Temperature  on  Individual 
Slopes,  also  Minima  During  Periods  of  Inversion 
and  Norm. — Altapass  (Table  2). — The  observations  on 
this  southeasterly  slope  show  the  highest  mean  minimum 
temperature  to  be  at  station  No.  2,  250  feet  above  station 
No.  1,  and  the  lowest  at  No.  5,  1,000  feet  above  No.  1, 
the  former  averaging  0.9°  higher  and  the  latter  1.9° 
lower  than  station  No.  1.  The  average  values  at  the 
stations  between  Nos.  2  and  5  show  a  gradual  decrease, 
No.  3  averaging  0.5°  higher,  and  No.  4,  1.4°  lower,  than 
No.  1.  Taking  these  values  as  a  basis,  it  is  apparent 
that  the  highest  average  minimum  temperature  on  the 
entire  slope  is  either  at  No.  2  or  slightly  above.  There 
is  a  considerable  monthly  variation  in  these  means, 
inversion  conditions  being  more  pronounced  usually  in 
the  autumn  months  than  in  any  other  season  of  the  year, 
this  being  due  to  a  combination  of  longer  nights  and 
longer  periods  of  clear  weather. 

During  the  critical  periods  of  spring  and  fall  the  entire 
slope  from  the  summit  down  to  No.  1  and  lower  is  usually 
free  from  white  frost,  except  on  small  benches,  but  with 


increasing  elevation  there  is  always  danger  from  top 
freeze,  the  temperature  at  No.  5  averaging  about  5° 
lower  than  No.  1  during  norm  conditions. 

On  the  other  side  of  the  Blue  Ridge  at  Altapass, 
called  the  Mitchell  County  side,  the  descent  is  very  slight, 
the  plateau  here  being  at  times  flush  with  the  top  of  the 
ridge.  As  would  be  expected,  heavy  frosts  are  observed 
frequently  on  the  plateau,  the  general  flatness  and  high 
elevation  being  ideal  for  great  loss  of  heat  by  radiation 
in  clear  weather. 

Unusual  fluctuations  in  temperature  at  Nos.  1  and  2 
during  anticyclonic  weather  indicate  the  development 
under  favorable  conditions  during  the  night  of  a  mountain 
breeze,  the  air  descending  from  the  high  plateau  through 
McKinney  Gap  (see  fig.  26.)  The  unusual  frequency  of 
northerly  winds  also  indicates  such  a  mountain  breeze. 

In  Table  2a  the  variation  in  average  temperatures  and 
differences  for  the  periods  of  inversion  weather  bear  a 
certain  relation  to  those  shown  in  Table  2.  However, 
the  differences  between  No.  1  and  the  stations  higher  up 
during  inversions  apparently  do  not  compare  with  those 


THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 


on  many  other  slopes,  simply  because  all  the  stations 
at  Altapass  are  located  high  up  above  the  valley  floor 
During  the  May  period  of  inversion,  with  light  southerly 
winds,  the  highest  minimum  is  shown  to  be  at  station 
JNo.  2,  250  feet  above  No.  1,  while  the  lowest  is  at  the 
summit,  1,000  feet  above  No.  1,  the  excess  at  the  former 
being  4.9°,  and  the  deficiency  at  the  latter  0.6°.  No.  2 
is  practically  in  the  middle  of  the  thermal  belt  during  this 
period. 

The  selected  November  period  of  inversions  with  light 
northerly  winds  shows  variations  between  the  base, 
slope,  and  summit  stations  similar  to  those  noted  in  the 
May  period,  but  in  a  lesser  degree,  as  this  period,  taken  as 
a  whole,  was  not  so  favorable  for  large  inversions  as  the 
period  in  the  spring.  Again,  the  influence  of  northerly 
winds  serves  to  lessen  the  differences  between  the  tem¬ 
peratures  at  the  various  stations,  as  these,  although 
gentle  to  light,  bring  the  colder  air  from  over  the  plateau 
on  the  edge  of  which  No.  5  is  situated  and  lower  the 
temperature  on  the  whole  slope,  as  shown  in  Table  2a. 

During  norm  conditions  (Table  2a)  a  different  situation 
is  apparent,  when  the  temperature  gradually  decreases 
from  the  base  to  the  summit,  roughly  speaking,  at  the 
rate  of  1°  for  about  200  feet.  In  both  inversions  and 
norm  conditions  the  lowest  temperature  at  Altapass  is 
on  the  average  at  the  summit,  and  this  is  consistent  with 
the  mean  minima  data  appearing  in  Table  2.  The 
warmest  station  during  periods  of  inversion  is  No.  2 
and  during  norm  conditions  is  No.  1. 


Table  2a. — Average  minimum  temperatures  during  selected  inversion 

and  norm  periods. 


Principal  and  slope  stations;  elevations  of 
base  stations  above  mean  sea  level,  feet. 

Height 
of  slope 
station 
above 
base 
(feet). 

Inver¬ 
sion- 
May  1-6, 
inclusive 
1913. 

Inver¬ 
sion — 
Nov.  2-5, 
inclusive, 
1916. 

Norm — 
Eight 
selected 
dates, 
January, 
February 
and 
March. 
1916J 

Altapass: 

No.  1,  Base  station,  elevation  2,230  . 

No.  2.  SE . 

250 

50.3 

55.2 

39.8 

42.5 

17.5 

16.4 

No.  3.  SE . 

500 

53.3 

40.8 

15.  5 

No.  4.  SE . 

750 

51.3 

39.5 

13.4 

No.  5.  Summit . 

1,000 

49.7 

39.5 

12.4 

Asheville: 

No.  1.  Base  station,  elevation  2,445 . 

No.  2.  N . 

155 

45.2 

51.2 

33.8 

38.2 

15.5 

13.5 

No.  2a.  S . 

155 

52.3 

41.8 

15.4 

No.  3.  N . 

380 

55. 2 

44.2 

13.4 

No.  3a.  S . 

Blantyre: 

No.  1.  Base  station,  elevation,  2,090 . 

No.  2.  NW . 

380 

56.2 

44.5 

14.1 

300 

39.0 

44.7 

29.0 

30.5 

20.5 

18.6 

No.  3.  NW . 

450 

51.2 

37.5 

17.6 

No.  4.  NW . 

600 

54. 2 

42.2 

17.9 

Blowing  Rock: 

39.2 

13.2 

No.  1.  Base  station,  elevation  3,130 . 

48.8 

No.  2.  S . 

450 

54.7 

45.2 

11.5 

No.  3.  SE . 

450 

39.5 

34.5 

10.9 

No.  4.  SE . 

625 

51.8 

42.0 

10.2 

No.  5.  SE . 

800 

52.2 

40.0 

8.8 

Bryson: 

No.  1.  Base  station,  elevation  1,S00 . 

39.7 

28.2 

18.1 

No.  2.  N . 

3.85 

45.0 

32.0 

17.5 

No.  2a.  S . 

385 

46.7 

31.8 

17.2 

No.  3.  Summit . 

570 

52.7 

36.2 

16.0 

Cane  River: 

No.  1.  Base  station,  elevation  2,650 . 

39.0 

27.0 

15.0 

No.  2.  N . 

190 

46.3 

35.0 

14.5 

No.  3.  NE . 

400 

50.7 

41.0 

13.1 

No.  4.  Summit . 

1,100 

56.7 

43.5 

9.5 

EUijay: 

No.  1.  Base  station,  elevation  2,240 . 

41.5 

30.0 

18.6 

No.  2.  N . 

310 

49.0 

34.0 

18.0 

No.  3.  N . 

620 

53. 3 

39.0 

15.6 

No.  4.  N . 

1,240 

58.  5 

46.5 

13. 6 

1,760 

45.0 

11. 5 

Globe: 

36.5 

23.6 

No.  1.  Base  station,  elevation  1,625 . 

44.8 

No.  2.  E . 

300 

54.3 

44.  2 

22. 1 

No.  3.  Summit . 

1,000 

61.7 

47.2 

18.0 

Gorge: 

No.  1.  Base  station,  elevation  1,400 . 

No.  2.  NE . 

290 

42.0 

43.5 

31.2 

33.0 

23.6 

22.5 

No.  3.  S . 

615 

52.3 

37.8 

20.9 

No.  4.  NE.  (old)  N.  (new) . 

840 

57.3 

47.0 

19. 0 

No.  5.  Summit . 1 

1,040 

04. 2 

49.5 

18.6 

Table  2a  —Average  minimum  temperatures  during  selected  inversion 
and  norm  periods — Continued. 


Norm- 


Principal  and  slope  stations;  elevations  of 
base  stations  above  mean  sea  level,  feet. 


Height 
of  slope 
station 
above 
base 
(feet). 


Inver¬ 
sion — 
May  1-6, 
inclusive, 
1913. 


Inver¬ 
sion— 
Nov.  2-5, 
inclusive, 
1916. 


Eight 

selected 

dates, 

January, 

February 

and 

March. 

1916J 


Hendersonville: 

No.  1.  Base  station,  elevation  2,200 . 

No.  2.  E . 

450 

600 

750 

No.  3.  E . 

No.  4.  Summit . 

Highlands: 

No.  1.  Base  station,  elevation  3,350 . 

No.  2.  SE . 

200 

325 

525 

725 

No.  3.  SE.  base  station . 

No.  4.  SE . 

No.  5.  SE . 

Mount  Ainu 

40.5 

47.5 
57.0 
58.3 


52.3 
55.7 

33.3 
53.0 
55.0 


29.5 
38.0 

43.2 

44.2 

40.8 

44.8 

22.5 

41.5 

43.2 


17.4 

16. 5 

15.1 

14.2 

16.6 

15.2 

13.4 

11.5 

10.6 


No.  1.  Base  station,  elevation  1,340 

No.  2.  W . 

No.  3.  E . 

No.  4.  Summit . 

Transon; 

No.  1.  Base  station,  elevation  2,970 

No.  2.  W . 

No.  3.  W . 

No.  4.  Summit . 

Tryon: 

'  No.  1.  Base  station,  elevation  950.. 

No.  2.  SE . 

No.  3.  SE . 

No.  4.  SE . 

Wilkesboro: 


160 

160 

360 


150 

300 

450 


380 

570 

1,100 


49.8 
62.0 

56.8 
63.3 

39.0 

53.2 

54.8 

56.8 

49.3 
63.7 
62.6 
62.2 


40.5 

47.8 

44.0 

48.0 


33.0 

42.2 

44.8 

44.8 

42.5 

50.5 
49.1 

43.5 


22.9 

21.1 

21.4 

20.2 


13.4 

12.5 

12.1 

11.5 


25.7 

24.6 

23.0 

20.5 


No.  1.  Base  station,  elevation  1,240. 

No.  2.  N . 

No.  3.  N . 

No.  4.  W . 


150 

350 

430 


46.2 

52.3 
57.7 


34.8 

42.8 

48.8  I 


58.3 


50.2 


23.9 

23.0 

23.2 

22.8 


1  Jan.  14  and  17,  Feb.  3  and  14,  Mar.  4,  8,  15,  and  16. 


Asheville  (Table  2). — From  the  base  station,  No.  1, 
the  average  minimum  temperature  on  the  north  slope 
increases  gradually  up  to  No.  3,  the  difference  between 
Nos.  1  and  2  and  between  Nos.  2  and  3  being  exactly  the 
same  for  the  four-year  period,  1.4°,  or  a  total  of  2.8° 
between  Nos.  1  and  3.  The  average  minima  on  the  south 
slope  from  No.  1  to  No.  3a  also  increase  with  elevation, 
but  the  differences  are  larger,  although  not  so  regular, 
as  on  the  north  slope,  No.  2a  averaging  2.5°,  and  No.  3a, 
3.1°,  higher  than  No.  1. 

It  should  be  understood  that  the  stations  above  the 
base  at  Asheville  are  at  the  same  elevation  on  two  slopes 
facing  each  other  and  inclosing  a  rather  narrow  valley. 
The  southerly  slope  is  much  steeper  than  the  northerly 
one,  as  shown  by  Figure  17. 

The  excess  in  mean  minimum  temperature  at  the  two 
highest  stations,  Nos.  3  and  3a,  over  the  base,  No.  1,  is 
greatest  in  May  and  November,  the  months  with  the  most 
frequent  and  largest  inversions.  There  is  a  remarkable 
uniformity  between  the  minimum  readings  at  the  two 
highest  stations  in  all  seasons  of  the  year.  In  fact,  there 
is  also  a  certain  uniformity  in  the  readings  at  Nos.  2  and 
2a.  The  table  below  contains  the  four-year  average 
minima  by  months  for  the  two  sets  of  stations  on  these 
opposite  slopes. 

Four-year  average  minima,  Asheville,  Nos.  2  and  2a  and  S  and  Sa, 
including  direction  of  slope  and  elevation  above  the  base. 


January. 

February. 

March. 

April. 

May. 

June. 

July, 
j  August. 

September. 

October. 

|  November, 
j  December. 

Annual. 

2,  N..  155  feet... 

33.3 

29.7 

33.0 

43.6 

52.9 

58.0 

61.4  60.4 

54.6 

45.9 

36.5  29.5 

45.0 

2a.  S.,  155feet.. . 

34.5 

30.6 

34.7 

45. 0 

53.9 

59.1 

62.4|  61.7 

55.7 

47.5 

37.0'  30.9 

46.1 

Difference . 

+  1.2 

+0.9 

+1.1 

+  1.4 

+1.0 

+  1.1 

+1. 0+1.3 

+1.1 

+  1.6 

+  1.1|  +  1.4 

+1.1 

3,  N.,  380  feet... 

33.9 

30.1 

34.1 

44.7 

54.9 

60.0 

63.2!  62.3 

55.6 

47.9 

38.8  30.8 

46.4 

3a,  S.,  380feet.. . 

34.5 

30.4 

34.4 

45.4 

55.2 

60.1 

63.4  62.6 

56.3 

48.4 

38. 8  30.8 

46.  7 

Difference . 

+0.6 

+0.3 

+0.3 

+0.7 

+0.3 

+0.1 

+0.2  +0.3 

+0.7 

+0.5 

0. 0  0. 0 

+0.3 

38 


SUPPLEMENT  NO.  19. 


This  table  shows  that  both  stations  on  the  southerly 
slope  have  higher  minima  than  on  the  northerly  slope 
throughout  the  year,  and  this  may  be  partly  due  to  the 
difference  in  direction  of  slope,  but  the  greater  steepness 
of  the  southerly  slope  is  the  main  factor.  Moreover,  the 
difference  in  minima  is  much  greater  between  Nos.  2 
and  2a  than  between  Nos.  3  and  3a.  The  differences  in 
the  minima  at  the  two  higher  stations  at  the  same  eleva¬ 
tion,  however,  are  slight,  and  no  seasonal  variation  is 
apparent,  but  even  here  the  advantage  is  with  No.  3a  on 
the  southerly  slope,  but  to  a  much  less  degree  than  at 
the  lower  level  at  No.  2a,  where  the  slope  is  steeper. 

The  differences  between  the  average  minima  at  Nos.  2 
and  2a  and  between  Nos.  3  and  3a  are  slight  as  compared 
with  the  differences  between  the  average  maxima, 
Tables  1  and  la.  The  maxima  at  the  upper  station, 
No.  3a,  on  the  south  slope  are  much  the  higher  during 
sunshiny  weather  at  all  seasons  of  the  year  and  at  No.  2a 
in  the  colder  months.  The  minimum  at  No.  3  averages 
almost  as  high  as  the  minimum  at  No.  3a,  even  though, 
because  of  the  shade  previously  referred  to  its  maxima 
are  much  lower.  In  spite  of  these  low  day  temperatures 
caused  by  shade  on  this  northerly  slope,  the  warm  free 
air  in  the  valley  on  nights  of  inversion  serves  to  prevent 
the  minimum  temperature  on  that  slope  from  falling 
appreciably  lower  than  on  the  opposite  southerly  slope. 

A  comparison  of  the  minimum  temperature  data  for 
the  selected  periods  of  inversion  (Table  2a)  indicates  that 
the  thermal  conditions  on  both  slopes  at  Asheville  are 
much  the  same  in  the  May  period,  but  that  they  differ  in 
the  November  period,  especially  at  the  elevations  of  Nos. 
2  and  2a.  Thus  in  May  stations  Nos.  2  and  2a  have  an 
average  excess  over  the  base  of  6°  and  7.1°,  respectively, 
while  Nos.  3  and  3a,  higher  up,  have  average  excesses  of 
10°  and  11°,  respectively,  in  each  case  there  being  a 
slight  advantage  in  minimum  temperature  on  the  steep 
southerly  slope.  In  the  November  period  the  advantage 
of  a  steep  southerly  exposure  is  especially  marked  at 
No.  2a.  Doubtless  the  center  of  the  thermal  belt  is 
located  on  the  slopes  at  a  level  considerably  higher  than 
Nos.  3  and  3a,  but  because  of  the  absence  of  additional 
stations  the  exact  level  can  not  be  determined. 

During  norm  conditions,  according  to  the  data  in 
Table  2a.,  the  stations  on  the  northerly  slope  are  re¬ 
latively  colder  than  those  on  the  southerly  slope,  but 
the  differences  between  the  base  station  and  those  higher 
up  are  never  great,  obviously  because  of  the  slight 
differences  in  elevation. 

Blantyre  (Table  2). — In  general  the  average  minima 
here  increase  from  the  base  No.  1  to  No.  4  on  the  summit. 
No.  1  is  some  distance  from  the  remaining  three  stations, 
which  are  located  on  the  slope  of  Little  Fodderstack 
Mountain,  No.  2  being  at  its  immediate  base.  In  the 
summer  months  the  differences  between  the  minima  at 
all  the  stations  are  small  as  compared  with  the  spring 
and  autumn  months,  especially  April,  May,  and  Novem¬ 
ber,  when  inversions  are  frequent.  In  November,  1913, 
the  average  minimum  at  No.  4  was  9.9°  higher  than  at 
No.  1,  and  8°  higher  than  at  No.  2.  In  the  summer,  the 
average  at  No.  2  is  often  lower  than  at  No.  1,  and  in 
July,  1916,  an  unusually  rainy  and  cloudy  month,  all 
stations  averaged  lower  than  No.  1.  The  month  of 
June,  1915,  also  cloudy  and  rainy,  shows  averages  with 
similar  differences. 

Station  No.  2  may  properly  be  considered  a  base 
station,  although  300  feet  higher  than  No.  1.  The 
larger  amount  of  vegetation  around  No.  2  as  compared 
with  No.  1  is  also  an  important  factor,  as  shown  by  the 
relatively  low  minima  at  the  former  during  the  warmer 


months,  when  the  vegetation  is  densest.  Moreover, 
during  these  months  the  differences  between  No.  1  and 
the  stations  higher  up  are  least  because  of  the  large 
amount  of  vegetation  in  the  orchard  as  compared  with 
the  closely  cropped  grass  around  No.  1  below  and  because 
of  the  small  range  of  inversion  usually  prevalent  during 
the  summer. 

The  considerable  differences  in  average  minima  be¬ 
tween  the  base  and  the  higher  stations  are  doubtless 
due  to  the  exceedingly  low  readings  at  the  lower  levels 
and  not  to  any  abnormally  high  readings  at  the  more 
elevated  stations.  The  valley  of  the  French  Broad  at 
Blantyre  is  rather  wide,  with  only  a  slight  descending 
grade,  and  is  inclosed  by  mountains  at  a  distance.  It  is 
much  like  a  vast  frost  pocket  with  opportunities  for  free 
radiation,  resulting  in  a  blanket  of  very  cold  air  at  the 
lower  levels.  In  fact,  considering  its  elevation  above 
sea  level,  station  No.  1  at  Blantyre  has,  together  with 
Bryson  No.  1  and  Gorge  No.  i,  the  lowest  average 
minima  of  all  the  stations  employed  in  the  research. 

In  the  selected  periods  of  inversion  (Table  2a)  the 
data  show  steadily  increasing  minima  from  the  valley 
floor  to  the  summit  of  Little  Fodderstack,  the  No.  4 
station  averaging  15.2°  higher  in  May  and  13.2°  higher 
in  November  than  No.  1.  The  center  of  the  thermal  belt 
at  such  times  would  be  above  the  elevation  of  the  summit 
station  were  the  slope  higher,  judging  from  a  comparison 
of  Blantyre  No.  4  with  the  summit  stations  at  Hender¬ 
sonville  and  Asheville,  which  average  from  2°  to  4° 
higher  than  Blantyre  during  these  periods. 

During  norm  conditions  at  Blantyre,  for  which  data 
are  given  in  Table  2a,  while  the  warmest  station  is  on 
the  valley  floor,  the  coldest  is  not  at  the  summit  but  on 
the  slope  at  No.  3,  150  feet  lower  down,  the  slight  average 
difference  of  0.3°  between  these  two  stations  possibly 
being  due  to  instrumental  error. 

Blowing  Rock  (Table  2). — Hexe  the  five  stations  are 
divided  into  two  groups,  Nos.  1  and  2  of  the  lower  group 
being  in  the  China  orchard  on  a  steep  southerly  slope  and 
Nos.  3,  4,  and  5  of  the  higher  group  in  the  Flat  Top 
orchard  on  a  moderate  southeasterly  slope  (fig.  30). 
Nos.  2  and  3,  although  in  different  orchards  about  one- 
half  mile  apart,  are  both  at  the  same  elevation,  450  feet 
above  No.  1. 

No.  2,  although  the  lowest  in  altitude,  is  not  a  valley 
floor  station,  while  No.  3  is  a  distinctly  valley  floor  station 
for  the  group  of  stations,  Nos.  3,  4,  and  5,  in  the  Flat  Top 
orchard.  It  is  for  these  reasons  that  the  differences  be 
tween  the  minima  at  station  No.  1  and  those  higher  up  do 
not  apparently  conform  to  the  differences  noted  in  the 
groups  at  Altapass,  Ashville,  and  Blantyre,  previously 
discussed. 

In  examining  the  figures  in  detail  by  individual  months 
we  find  that  in  the  months  of  November  and  December, 
1916,  and  April,  1915,  No.  2  averages,  respectively,  3.9°, 
3.3°,  and  2.8°  higher  than  No.  1,  while  in  September,  1913, 
a  cold  and  more  or  less  cloudy  month,  No.  2  averages  1.2° 
lower  than  No.  1.  Aside  from  the  fact  that  the  largest 
inversions  occur  in  April,  May,  and  November,  there  does 
not  seem  to  be  any  regularity  as  to  the  occurrences  of 
positive  or  negative  differences  between  Nos.  1  and  2. 
On  November  4,  1916,  No.  2  was  10°  higher  than  No.  1, 
while  negative  differences  of  8°  and  9°  were  noted  on  in¬ 
dividual  days  in  the  months  of  December,  1916,  and 
April,  1915. 

These  great  differences  depend  almost  entirely  upon 
the  direction  and  velocity  of  the  wind,  as  from  an  ex ami- 
nation  of  the  Blowing  Rock  contour  map,  Figure  30,  it  is 
evident  that  under  favorable  conditions  the  topography 


39 


THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 


aids  greatly  in  developing  a  breeze  down  the  slope  at 
night,  which  in  this  region  is  an  exchange  of  air  between 
the  cold  plateau  to  the  north  of  the  China  and  Flat  Top 
orchards  and  the  warmer  descending  ridges  and  spurs  of 
the  valley  of  the  Johns  River  and  the  Middle  Fork  of  the 
New  River.  On  nights  when  this  wind  blows,  No.  2 
located  near  the  top  of  the  plateau  and  450  feet  above 
No.  1,  averages  colder  than  the  base  station,  while  on 
nights  when  this  wind  is  not  developed  particularly 
during  the  prevalence  of  light  southerly  winds  which  are 
sufficient  to  check  the  flow  of  cold  air  from  the  plateau, 
there  are  large  inversions  between  Nos.  1  and  2. 

All  of  the  stations  in  the  Flat  Top  orchard  show  average 
minima  lower  than  those  in  the  China  orchard,  and  this 
should  be  expected,  as  the  Flat  Top  orchard  is  a  partly 
inclosed  basin  with  only  a  very  slight  slope  at  the  open 
end,  furnishing  conditions  favorable  for  a  frost  pocket. 
No.  3,  the  base  station  in  the  Flat  Top  orchard,  has,  of 
course,  the  lowest  minimum,  the  average  being  3.8°  lower 
than  No.  1  in  the  China  orchard.  At  No.  3  is  found  the 
lowest  average  minimum  temperature  of  all  the  experi¬ 
mental  stations,  except  Highlands  No.  3,  which  is  also 
located  in  a  frost  pocket,  but  of  a  different  character. 

As  in  the  China  orchard,  so  in  the  Flat  Top  orchard, 
there  is  evidence  of  a  mountain  breeze  which  occurs  under 
exactly  the  same  conditions,  but  on  nights  when  No.  2 
is  colder  than  No.  1  the  minimum  at  No.  5  is  not  lower 
than  No.  3,  although  the  excess  at  No.  5  over  No.  1  is 
greatly  reduced  during  the  prevalence  of  this  breeze, 
and,  taking  the  temperature  at  these  stations  hour  by 
hour  on  such  nights,  No.  5  is  actually  colder  than  No.  3 
by  several  degrees. 

During  both  selected  periods  of  inversion  (Table  2a) 
No.  2  averages  6°  higher  than  No.  1.  Nos.  4  and  5  in 
the  Flat  Top  orchard  average,  respectively,  12.3°  and 
12.7°  higher  than  No.  3,  its  base  station,  in  May  and  7.5° 
and  5.5°  higher  in  November,  although  their  respective 
elevations  above  No.  3  are  only  175  and  350  feet.  These 
differences  in  temperature  are  exceptionally  large  when 
the  slight  differences  in  elevation  are  considered.  The 
minimum  temperature  at  No.  3  in  the  Flat  Top  orchard 
during  the  Ma}^  period  averages  15.2°  lower  than  No.  2 
in  the  China  orchard,  although  both  stations  have 
exactly  the  same  elevation. 

The  effect  of  wind  direction  and  velocity  is  again 
apparent  in  comparing  the  average  differences  in  minima 
between  Nos.  3  and  5,  as  shown  in  the  two  selected  periods. 
During  the  week  in  May  with  light  southerly  winds  the 
temperature  at  No.  5  exceeds  that  at  No.  3  by  an  average 
difference  of  12.7°,  and  on  these  nights  the  upper  limit 
of  the  thermal  belt  probably  extended  above  No.  5.  In 
November,  when  the  prevalence  of  the  breeze,  aided  on 
some  nights  by  northerly  winds,  increases  the  tem¬ 
perature  at  No.  3  and  lowers  it  at  No.  5,  the  difference 
is  reduced  to  5.5°,  and  the  middle  of  the  thermal  belt  on 
these  nights  is  probably  close  to  No.  4.  Of  course,  during 
this  same  period  conditions  were  favorable  for  a  breeze 
down  the  slope  of  the  other  orchard  where  Nos.  1  and  2 
are  located,  but  no  effect  upon  the  temperature  condi¬ 
tions  was  apparent  in  the  average  difference  between 
these  two  stations,  because  on  one  of  the  nights  included, 
November  4,  the  excess  of  No.  2  over  No.  1  was  so  marked, 
10°,  that  the  deficiencies  on  the  other  nights  were  neu¬ 
tralized  in  the  averages. 

During  the  selected  norm  period  the  temperature  in 
each  orchard  decreases  regularly  with  elevation,  but,  as 
is  usually  the  case  because  of  its  exposure,  No.  3  in  the 
Flat  Top  orchard  has  a  somewhat  lower  temperature 
than  No.  2  in  the  China  orchard. 


Bryson  (Table  2) . — The  average  minimum  temper¬ 
ature  at  the  Bryson  base  station,  No.  1,  is  rather  low  and 
agrees  closely  with  that  at  the  base  station  at  Blantyre, 
which  has  a  slightly  higher  elevation,  the  average  minima 
for  the  four-year  period  being  41.  9°  and  41. 8°,  re¬ 
spectively.  These  values  are  both  low  for  the  altitude, 
and  this  is  due  to  the  fact  that  both  stations  are  located 
close  to  a  rather  wide  valley  floor  with  conditions  re¬ 
sembling  a  large  frost  pocket.  The  average  minima  at 
the  more  elevated  stations  at  Bryson,  Nos.  2  and  2a,  on 
the  north  and  south  slopes,  respectively,  both  at  an 
elevation  of  385  feet  above  the  base,  and  at  No.  3  on 
the  summit,  with  an  elevation  of  570  feet,  are  consistently 
higher.  While  the  average  excess  at  No.  2  on  the  north 
slope  over  No.  1  is  1.1°,  that  at  No.  2a  on  the  south 
slope  is  greater,  1.7°,  there  being  an  average  difference 
of  0.6°  between  the  two  slope  stations.  The  difference 
between  No.  1  and  the  summit  station  No.  3  is  2.7°. 

The  great  radiating  surfaces  of  the  mountains  sur¬ 
rounding  the  Bryson  region  on  nearly  all  sides  serve  to 
intensify  the  cooling  of  the  lower  layers  of  the  atmos¬ 
phere,  thus  causing  during  nights  of  inversion  much  lower 
minima  at  No.  3  than  would  be  expected,  considering  its 
position  at  the  summit  of  a  small  knob.  Even  so,  it  is 
then  warm  as  compared  with  No.  1  on  the  valley  floor. 

The  table  below  shows  the  mean  monthly  and  annual 
minimum  temperatures  at  stations  Nos.  2  and  2a  on  the 
northerly  and  southerly  slopes,  respectively,  for  the 
entire  four-year  period,  together  with  the  differences. 
While  the  average  yearly  difference  is  only  0.6°,  the 
monthly  variation  is  irregular,  the  southerly  slope 
averaging  higher  in  all  months  with  the  exception  of 
October,  in  which  month  it  is  0.1°  lower.  In  July  the 
minimum  on  the  southerly  slope  averages  1.4°  higher 
than  the  station  on  the  other  slope,  this  being  the  greatest 
four-year  average  monthly  difference. 

Four-year  average  minima,  Bryson,  Nos.  2  and  2a,  including  direction 
of  slope  and  elevation  above  the  base. 


January. 

February. 

March. 

April. 

May. 

June. 

>> 

3 

►“5 

August. 

September. 

October. 

November. 

December. 

!  Annual. 

No.  2,  N.,  385 
feet . 

32.6 

28.6 

29.5 

41.3 

49.7 

56.0 

59.8 

59.6 

53.0 

44.2 

33.6 

27.9 

43.0 

No.  2a,  S.,  385 
feet . 

33.1 

29.0 

29.8 

42.4 

50.6 

56.8 

61.2 

60.6 

53.3 

44.  1 

33.7 

28.2 

43.6 

Difference . 

+  0.5 

+0.4 

+0.3 

+1.1 

+0.9 

+0.S 

+  1.4 

+1.0 

+0.3 

-0.1 

+0.1 

+0.3 

+0.6 

The  relatively  higher  minima  at  No.  2a  may  be  partly 
due  to  its  southerly  exposure.  Prevailing  wind  direction 
is  also  a  consideration. 

During  the  selected  periods  of  inversion  (Table  2a) 
the  thermal  belt  at  Bryson  is  quite  pronounced.  In 
May,  station  No.  2a  on  the  southerly  slope,  with  an  ele¬ 
vation  of  385  feet,  has  an  average  mean  of  7°  higher  than 
the  base  and  1.7°  higher  than  station  No.  2,  with  the 
same  elevation  on  the  northerly  slope.  The  summit 
station,  185  feet  higher  up,  has  a  mean  of  13°  higher  than 
the  base,  and  the  thermal  belt  during  these  periods  would 
doubtless  be  centered  above  the  elevation  of  the  summit 
station  here  as  at  Blantyre  and  Asheville  were  this  slope 
higher  up. 

It  will  be  noted  that  in  the  November  period  the  in¬ 
crease  in  temperature  with  increase  in  elevation  is  not 
so  decided  as  that  recorded  in  May,  and  aside  from  the 
fact  that  the  former  period,  as  a  whole,  was  not  so  favor¬ 
able  for  large  inversions  as  the  week  in  May,  the  decreased 
differences  between  the  various  stations  in  November  are 
due  to  the  effect  of  northerly  winds. 


40 


SUPPLEMENT  NO.  19. 


During  norm  conditions  the  variation  in  temperature 
has  no  special  features,  the  decrease  with  elevation  being 
approximately  the  amount  usually  observed. 

Cane  River  (Table  2). — While  the  maxima  at  Cane 
River  have  some  unusual  characteristics,  especially  as 
regai’ds  the  rather  low  readings  in  the  cove  at  station 
No.  3  and  high  readings  at  No.  4,  as  shown  in  Tables  1 
and  la,  the  minima  also  are  not  entirely  free  from  irregu¬ 
larities.  For  instance,  the  minimum  at  No.  2,  on  a 
northerly  slope  190  feet  above  the  base  station  No.  1, 
averages  the  higher  by  as  much  as  2.4°,  but  the  increase 
in  temperature  above  that  point  is  very  slight,  the  aver¬ 
age  at  No.  4,  the  summit  station,  being  only  3.1°  more 
than  that  at  the  base.  However,  these  values  are,  as  a 
matter  of  fact,  consistent  when  we  consider  that  both 
nights  of  inversion  and  norm  are  involved. 

The  thermal  conditions  at  Cane  River  during  nights  of 
inversion  are  quite  marked,  as  shown  by  the  averages 
for  the  selected  periods  (Table  2a),  largely  because  of  the 
absence  of  opposing  slopes  close  by.  At  the  summit 
station,  No.  4,  with  an  elevation  of  1,100  feet  above  the 
base,  the  average  excess  in  minimum  temperature  over 
No.  1  in  May  is  17.7°,  with  several  individual  differences 
of  20°  or  more,  while  at  Nos.  2  and  3,  190  and  400  feet 
above  the  base  station,  the  average  excesses  for  the  same 
month  are  7.3°  and  11.7°,  respectively.  These  large  dif¬ 
ferences  between  No.  1  and  the  slope  stations  Nos.  2  and 
3  are,  of  course,  unusual  considering  the  elevation. 

The  differences  between  Nos.  1  and  3  are  more  pro¬ 
nounced  in  November  than  in  May,  and  this  is  due  to 
the  effect  of  the  northerly  winds  during  the  November 
period.  As  the  slope  at  Cane  River  Faces  the  north, 
winds  from  this  direction,  even  though  light,  cause 
higher  temperatures  at  Nos.  2  and  3. 

The  variation  during  norms  is  consistent  with  the  de¬ 
crease  in  elevation,  the  decrease  in  temperature  being 
quite  regular  and  much  the  same  as  on  other  slopes. 

Ellijay  (Table  2).- — Here  we  have  a  group  of  five  sta¬ 
tions  on  a  northerly  slope  ranging  from  the  base,  with 
an  elevation  of  2,240  feet  above  sea  level,  to  the  summit, 
with  an  elevation  of  4,000  feet.  This  slope  has  been 
referred  to  previously  as  one  more  nearly  approaching 
the  ideal,  as  it  is  not  broken  up  into  coves  and  frost 
pockets,  the  descent  being  more  or  less  regular  from  the 
summit  to  the  base. 

Of  the  average  minimum  values  (Table  2)  No.  4,  with 
an  elevation  of  1,240  feet  above  the  base,  is  the  highest, 
the  excess  over  No.  1  being  4.2°.  No.  3  has  an  excess 
of  2.8°  and  No.  5,  at  the  summit,  520  feet  above  No.  4, 
an  excess  of  3.3°.  These,  of  course,  represent  only  aver¬ 
age  conditions,  and  when  we  realize  that  during  norm 
conditions  the  summit  station  invariably  is  considerably 
colder  than  No.  4  we  must  conclude  that  during  nights 
of  inversion  the  minimum  at  No.  5  is  relatively  high.  As 
a  matter  of  fact,  while  the  center  of  the  thermal  belt  at 
Ellijay  is  usually  not  far  below  the  summit,  inversions 
noted  here  are  not  so  pronounced  as  those  observed  at 
Cane  River. 

Although  the  summit  station,  No.  5,  1,760  feet  above 
the  base,  was  not  in  operation  in  1913  during  the  selected 
period  of  inversion  in  May  included  in  Table  2a,  the  aver¬ 
ages  in  the  November  period  bring  out  clearly  the 
thermal  conditions  at  that  level,  as  well  as  at  the  other 
stations  on  this  slope,  there  being  a  steady  increase  up 
to  No.  4,  with  No.  5  averaging  1.5°  lower  than  No.  4, 
but  nevertheless  15°  higher  than  No.  1.  As  No.  4  has 
an  average  excess  of  17.0°  in  the  May  period,  it  is  prob¬ 
able  that  the  thermal  belt  was  close  to  the  summit. 
In  fact,  sometimes  during  these  inversion  periods  the 


temperature  is  highest  at  the  summit,  but  it  is  never¬ 
theless  most  frequently  the  highest  at  No.  4.  This 
excess,  17.0°  at  the  elevation  of  1,240  feet  above  the 
base,  is  about  the  same  as  that  at  the  summit  station 
at  Cane  River,  which  has  during  the  same  period  an 
excess  of  17.7°  for  an  elevation  of  1,100  feet. 

During  norm  conditions  the  temperature,  of  course, 
is  steadily  lower  from  the  base  to  the  summit,  and  the 
averages  shown  in  Table  2a  conform  to  the  variation  at 
other  points,  considering  the  marked  differences  in 
elevation. 

Globe  (Table  2). — The  stations  in  this  group  are  only 
three  in  number,  No.  2  being  300  feet  and  No.  3  1,000 
feet  above  No.  1,  the  base  station,  and  because  of  the 
wide  gap  between  the  two  upper  stations  the  tempera¬ 
ture  conditions  on  the  slope  can  not  be  clearly  defined. 

The  average  minima  here  (Table  2)  generally  increase 
from  No.  1  to  No.  3,  although  in  the  colder  months  of 
the  year  there  is  very  little  difference  between  Nos.  2 
and  3,  and  not  infrequently  No.  3  is  lower  than  No.  2. 

During  nights  of  inversion  the  temperature  at  Globe 
No.  2  is  unusually  high  considering  its  elevation  above 
the  valley  floor,  300  feet,  and  during  the  selected  period, 
November  2-5,  1916  (Table  2a),  the  minimum  tempera¬ 
ture  averaged  44.2°,  while  near  by  at  Gorge  No.  2, 
290  feet  above  its  base,  the  temperature  averaged  33°. 

The  variation  in  minimum  temperature  during  norm 
conditions  needs  hardly  any  special  reference,  as  its  rate 
of  decrease  does  not  seem  to  differ  materially  from  that 
observed  elsewhere. 

Gorge  (Table  2). — The  four-year- average  minima  rep¬ 
resent  fairly  well  the  differences  existing  between  the 
various  stations  during  each  month.  In  no  month 
during  the  research  is  the  average  at  No.  5,  the  summit 
station,  lower  than  that  at  No.  1,  the  base,  there  being 
a  steady  increase  in  all  months  from  station  No.  2  to  the 
summit.  The  average  difference  between  Nos.  1  and  2 
is  only  slight,  the  latter  in  some  months  averaging  the 
lower,  situated  as  it  is  in  a  cove  on  a  gradual  slope.  In 
December,  1914,  and  July,  1916,  both  cold  and  wet 
months  and  with  few  nights  of  inversion,  there  was 
practically  no  difference  between  Nos.  1  and  5. 

Inversions  at  Gorge  are  exceedingly  well  marked, 
and  during  several  of  the  individual  months  in  the  four- 
year  period  the  minimum  at  No.  5  averaged  from  7°  to 
11°  above  No.  1,  and  on  somo  nights  differences  ranging 
from  15°  to  20°  were  registered.  An  inversion  of  24® 
was  noted  between  Nos.  1  and  5  on  May  22,  1914,  and 
also  on  November  27  of  the  same  year;  and  at  6  a.  m. 
November  13,  1913,  there  occurred  the  extreme  inversion 
of  31°.  On  this  date  the  difference  in  the  minima  was 
but  16°,  the  temperature  at  No.  1  falling  from  29°  at  9 
p.  m.  on  the  12th  to  26°,  the  minimum,  at  6  a.  m.  of  the 
13th,  while  during  this  same  interval  the  temperature 
at  No.  5  rose  from  42°,  the  minimum,  to  57°. 

Although  the  position  of  station  No.  4  was  changed 
at  the  close  of  1914  from  the  north  slope  to  a  point  on  the 
northeast  slope  having  the  same  elevation  above  the 
base,  the  average  minima  as  compared  with  the  base 
station  do  not  vary  considerably.  The  old  station 
averages  somewhat  lower  than  the  new  one.  The  mean 
minimum  temperature  at  the  old  No.  4  for  the  two  years 
1913  and  1914  is  2.8°  higher  than  the  base  station,  while 
that  at  the  new  location  for  the  two  years  1915  and  1916 
is  3.4°  higher  than  the  base  station,  the  difference  in  the 
excesses  being  0.6°. 

During  the  selected  periods  in  May  and  November 
(Table  2a)  the  inversion  conditions  are  seen  to  be  quite 
pronounced  at  Gorge,  there  being  a  slight  rise  from  the 


41 


THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 


base  to  station  No.  2,  and  thence  a  rapid  rise  to  the 
summit.  The  averages  at  the  summit  for  the  May  and 
November  periods  were  22.2°  and  18.3,  respectively,  higher 
than  the  base,^  although  the  difference  in  elevation  is  only 
1,040  feet.  This  rate  of  increase  is  even  greater  than 
that  at  Cane  River,  Ellijay,  or  Globe  for  the  same  periods. 
No.  2  partakes  largely  of  valley  floor  conditions,  and  it  is 
nearly  as  cold  as  No.  1  during  the  May  and  November 
periods  of  inversion. 

No.  3  is  affected  by  the  hills  close  by,  not,  of  course,  in 
the  same  degree  as  No.  2,  but  considerably,  nevertheless, 
as  indicated  by  the  small  increases  at  that  level,  615  feet, 
during  inversion  conditions,  as  compared  with  stations 
at  approximately  the  same  level  at  other  places. 

,  It  is  because  of  the  great  increase  in  temperature  at  the 
higher  levels  during  nights  of  inversion  that  the  average 
minimum  is  relatively  so  high  at  the  upper  stations.  In 
fact,  the  four-year-average  excess  in  minimum  tempera¬ 
ture  of  4.5°  at  No.  5  over  the  base  station  at  Gorge,  as 
shown  in  Table  2,  is  the  greatest  noted  on  any  slope. 

The  decrease  in  temperature  with  elevation  during 
norm  conditions  is  regular  and  does  not  vary  to  any 
extent  from  the  decrease  observed  on  other  slopes. 

Hendersonville  (Table  2). — The  four-year  averages  in 
these  tables  represent  fairly  well  the  situation  at  Hen¬ 
dersonville.  The  differences  in  minima  between  the 
various  stations  are  large  considering  the  slight  differ¬ 
ences  in  elevation,  and  this  is  due  to  the  great  variation 
in  temperature  during  nights  of  inversion. 

Station  No.  1,  located  on  a  nearly  level  surface  some 
distance  from  the  base  of  Jump  Off  Mountain,  is  a  rather 
cold  place  (see  fig.  13).  No.  2  is  on  a  bench  or  flat  plot 
on  the  northeast  slope  of  the  mountain,  where  there  is 
a  better  exchange  of  air  on  nights  when  the  wind  is  from 
a  northerly  quarter  than  from  other  directions.  On 
nights  with  large  inversions  at  No.  2  the  general  move¬ 
ment  of  the  air  is  from  the  north,  and  on  nights  when  the 
inversions  are  small  between  Nos.  1  and  2,  but  large 
between  Nos.  1  and  4,  the  wind  is  invariably  from  the 
south.  Thus  the  barrier  to  the  south  allows  the  cold  to 
accumulate  at  No.  2,  while  the  greater  freedom  of  ex¬ 
change  with  a  northerly  wind  retards  the  loss  of  heat. 
Later  under  the  caption  “Inversions”  the  effect  of  wind 
direction  upon  the  temperature  on  this  slope  will  be 
brought  out  in  detail  (see  fig.  62). 

During  the  selected  periods  of  inversion  (Table  2a) 
there  is  a  pronounced  increase  in  temperature  from  the 
base  to  the  summit.  Moreover,  the  increase  is  relatively 
as  great  in  the  lower  as  in  the  higher  levels  so  far  as  the 
observations  show,  there  being  in  May  an  excess  of  7°  at 
No.  2,  with  an  elevation  of  450  feet  above  the  base. 
Again,  between  Nos.  2  and  4,  with  a  difference  in  eleva¬ 
tion  of  300  feet,  the  average  increase  in  temperature  in 
the  May  period  is  10.8°,  while  the  average  excess  at  the 
summit,  station  over  the  base,  for  a  difference  in  eleva¬ 
tion  of  750  feet,  is  17.8°,  both  excesses  being  truly  re¬ 
markable.  In  the  November  period  the  relatively  large 
inversion  at  No.  2  is  due  to  the  effect  of  the  northerly 
winds  in  favoring  freedom  of  exchange  with  the  warm 
free  air,  as  stated  above. 

The  differences  in  temperature  from  base  to  summit 
during  norms  are  fairly  uniform  and  much  the  same  as  at 
the  other  places. 

Highlands  (Table  2).— Here  we  have  the  highest  group 
of  stations  in  the  entire  research — in  two  different  or¬ 
chards,  the  Satulah  and  the  W  aldlieim.  The  Satulah 
orchard,  in  which  Nos.  1  and  2  are  located,  is  rather 
warm,  considering  its  elevation,  doubtless  because  of  its 
location  on  a  southerly  slope  and  immediately  under 


Mount  Satulah,  which  towers  above  to  the  north  and 
northeast.  A  vast  amount  of  heat  is  undoubtedly  radi¬ 
ated  from  this  rock  to  the  orchard  below,  and  No.  2, 
closest  to  the  rock,  naturally  has  the  highest  temperature, 
maximum  as  well  as  minimum. 

However,  the  minimum  at  No.  2  does  not  average  uni¬ 
formly  higher  than  No.  1,  because  in  cloudy  or  wet  weather 
the  normal  rate  of  decrease  with  elevation  prevails.  But 
in  months  haying  frequent  nights  of  inversion  the  aver¬ 
age  at  No.  2  is  considerably  higher  than  at  No.  1.  In 
the  month  of  February,  1915,  the  minimum  at  No.  2  was 
frequently  10°  higher  than  the  minimum  at  No.  1. 

The  Waldheim  orchard,  on  Dog  Mountain,  with  some¬ 
what  higher  elevation  and  distant  a  couple  of  miles  from 
Mount  Satulah,  is  much  colder.  The  mean  minimum  for 
the  four-year  period  at  No.  3,  the  base  station  of  this 
orchard,  is  8.1°  below  the  average  at  No.  1  of  the  Satulah 
orchard,  and  is,  in  fact,  the  lowest  average  of  all  the  sta¬ 
tions  employed  in  this  research,  due  to  its  peculiar  ex¬ 
posure  and  its  elevation  above  sea  level. 

The  minima  at  No.  3  are  the  special  feature  of  the 
Waldheim  orchard,  as  those  at  Nos.  4  and  5  are  not 
unusual,  considering  the  elevation,  nor  is  there  generally 
much  difference  between  the  minima  at  the  two  higher 
stations.  No.  3  is  in  a  typical  frost  pocket  in  a  small 
basin  at  the  foot  of  the  slope  on  which  the  orchard  is 
located  and  is  surrounded  on  all  other  sides  by  heavy 
timber.  A  relatively  large  area  of  radiating  surface  here 
permits  rapid  loss  of  heat  on  nights  favorable  for  inver¬ 
sion,  and  convective  exchanges  are  impossible. 

During  the  selected  periods  (Table  2a)  marked  inver¬ 
sions  are  noted  in  both  the  Satulah  and  Waldheim 
orchards.  The  large  inversions  in  the  Waldheim 
orchard  are  due  more  to  the  very  low  minima  observed 
at  No.  3,  its  base  station,  than  to  high  minima  on  the 
slope  at  Nos.  4  and  5.  The  minima  at  No.  3  at  High¬ 
lands  during  the  May  period  average  33.3°,  which  is  19° 
lower  than  No.  1  in  the  Satulah  orchard,  and  it  is  not 
strange  that  a  marked  inversion  is  noted  during  this 
period  at  Nos.  4  and  5.  At  the  former  we  have  an  excess 
over  the  base  of  19.7°  in  the  May  and  19°  in  the  November 
period  for  a  difference  in  elevation  of  200  feet,  and  this 
rate  of  increase  in  average  minimum  temperature  between 
Nos.  3  and  4  is  the  greatest  observed  on  any  slope  in  this 
region  during  this  period  of  inversion.  For  the  next  200 
feet,  from  No.  4  to  No.  5,  the  increase  in  temperature  is 
not  important,  so  that  the  main  feature  of  the  thermal 
conditions  in  the  Waldheim  orchard  is  the  increase  from 
No.  3  to  No.  4. 

The  decrease  in  temperature  during  norm  conditions 
at  Highlands  conforms  generally  to  the  situation  in  other 
portions  of  the  region. 

Mount  Airy  (Table  2). — The  group  of  stations  at  this 
place,  having  a  much  lower  elevation  than  those  in  the 
main  mountain  region,  naturally  do  not  have  so  low 
minima  during  critical  periods.  The  base  station,  No.  1, 
at  Mount  Airy  averages  the  lowest  of  the  group,  as  else¬ 
where.  No.  2,  on  the  rather  steep  west  slope  with  an 
elevation  of  160  feet  above  the  base,  shows  the  highest 
average  minima — in  fact,  1°  higher  than  No.  3  on  the 
east  slope  at  the  same  elevation.  This  is  as  we  would 
expect,  because  of  the  comparative  steepness  at  No.  2 
and  its  westerly  exposure.  A  westerly  exposure  having 
the  benefit  of  direct  sunshine  during  the  warmest  period 
of  a  clear  day,  the  free  air  on  that  slope  is  warmer  than  on 
the  easterly  side,  and  a  station  there  has  usually  both  a 
higher  maximum  and  minimum  temperature  than  an 
easterly  slope.  The  summit  station,  No.  4,  200  feet 
higher  up  on  the  ridge  and  located  between  Nos.  2  and  3, 


42 


SUPPLEMENT  NO.  19. 


has  an  average  minimum  midway  between  the  two  on  the 
slope. 

The  table  below  gives  the  average  monthly  and  annual 
minimum  temperatures  for  Nos.  2  and  3,  on  the  west  and 
east  slopes  at  the  same  elevation,  with  the  differences 
between  the  two.  While  No.  3  averages  1°  lower  for  the 
entire  four  years,  there  are  some  months  in  which  the  dif¬ 
ferences  are  much  greater,  the  greatest  being  2°  in  No¬ 
vember,  which  month,  along  with  May  and  October,  is 
characterized  by  a  large  number  of  inversions.  The 
months  with  few  inversions  and  cloudy  weather,  Janu¬ 
ary,  February,  March,  and  December,  have  only  small 
differences  between  Nos.  2  and  3. 


Four-year  average  minima,  Mount  Airy,  Nos.  2  and  3,  including  direc¬ 
tion  of  slope  and  elevation  above  the  base. 


January. 

February. 

March. 

April. 

1 

May. 

June. 

July. 

August. 

September. 

October. 

November. 

December. 

Annual. 

No.  2,  W.,  160 
feet . 

34.3 

31.4 

35.6 

47.2 

57.2 

63.1 

66.3 

64.7 

58.8 

51.3 

41.0 

32.2 

48.6 

No.  3,  E.,  160 
feet . 

34.0 

30.8 

35.3 

46.4 

55.6 

61.8 

64.7 

64.0 

57.6 

49.7 

39.0 

31.8 

47.6 

Difference . 

-0.3 

-0.6 

-0.3 

-0.8 

-1.6 

-1.3 

-1.6 

-0.7 

-1.2 

-1.6 

-2.0 

-0.4 

-1.0 

The  mean  minima  during  the  selected  periods  of  inver¬ 
sion  (Table  2a)  indicate  that  the  thermal  conditions  at 
Mount  Airy  are  most  unusual,  especially  at  No.  2  at  the 
160-foot  level  on  the  west  slope,  where  there  was  an 
average  excess  in  minimum  temperature  over  the  base  of 
12.2°  in  the  May  period,  thus  emphasizing  the  effect  upon 
the  minimum  temperature  during  nights  of  inversion  of  a 
westerly  location  and  a  steep  slope.  This  difference  is 
much  greater  than  that  noted  in  the  same  periods  between 
Nos.  2  and  2a,  Asheville,  which  have  a  corresponding  ele¬ 
vation  above  the  base  station,  but  not  so  great  as  noted  at 
Transon  No.  2,  somewhat  similarly  situated  as  regards  its 
base  station.  The  summit  station  No.  4  at  Mount  Airy, 
200  feet  above  No.  2,  has  an  average  excess  of  13.5°  over 
the  base  station.  This  in  itself  is  exceptionally  large,  but 
the  principal  feature  is  the  excess  at  No.  2.  The  figures 
in  the  November  period  follow  closely  those  in  May  as  far 
as  variation  is  concerned,  although  the  actual  values  are 
lower,  as  should  be  expected. 

The  conditions  prevalent  at  Mount  Airy  during  the 
norm  period,  as  shown  by  Table  2a,  are  somewhat  abnor¬ 
mal,  the  average  rate  of  decrease  in  minima  between  base 
and  summit  being  2.2°  for  300  feet. 

Transon  (Table  2). — The  group  here  has  a  considerable 
altitude  above  sea  level,  but  with  only  slight  differences 
between  the  various  stations.  Moreover,  the  slope  is 
gentle  and  not  steadily  upward,  there  being  two  or  three 
knolls  and  corresponding  depressions,  as  shown  by  the 
profile  in  Figure  37. 

The  four-year  averages  in  minimum  temperature  are 
fairly  representative  of  the  variations  throughout  the 
different  months  of  the  year,  although  in  the  colder 
months  there  is  little  difference  between  Nos.  3  and  4. 
However,  No.  1  is  always  the  coldest,  as  in  no  month 
during  the  entire  four  years  does  any  other  station  here 
average  lower. 

During  the  selected  periods  of  inversion  (Table  2a) 
the  increase  in  temperature  on  the  slope  is  most  marked; 
in  fact,  considering  the  slight  differences  in  elevation 
between  the  various  stations,  the  average  inversion 
during  the  May  period  is  one  of  the  greatest  observed 
during  the  research,  and  this  applies  especially  to  the 
large  difference  of  14.2°  between  the  base  station,  No.  1 


and  No.  2  on  the  west  slope,  150  feet  higher  up.  While 
this  difference  is  not  so  large  as  that  observed  between 
the  two  lower  stations  in  the  Waldheim  orchard  at  High¬ 
lands,  the  excess  is  greater  than  that  noted  at  No.  2, 
Mount  Airy,  somewhat  similarly  situated,  and  it  is  more 
than  twice  as  great  as  that  between  Nos.  1  and  2  at 
Wilkesboro,  which  have  the  same  difference  in  elevation, 
although  the  No.  2  station  there  is  on  a  north  slope 
instead  of  a  west  slope,  as  at  Transon. 

During  norm  conditions  the  rate  of  decrease  in  tempera¬ 
ture  from  the  base  to  summit  at  Transon  is  apparently 
close  to  the  average  for  the  region. 

Tryon  (Table  2) . — While  the  base  station  at  Tryon  has 
the  least  altitude  above  sea  level  of  all  employed  in  the 
research,  950  feet,  No.  4  is  1,100  feet  above  on  Warrior 
Mountain,  so  that  on  this  slope  there  is  a  considerable 
range  in  elevation. 

The  mean  minimum  temperature  decreases  regularly 
from  No.  2  to  No.  4,  there  being  no  month  in  the  four 
years  in  which  No.  3  is  not  lower  than  No.  2  and  in  which 
No.  4  is  not  lower  than  No.  3.  In  this  respect  Tryon 
differs  from  all  the  other  groups  of  stations,  except  pos¬ 
sibly  Altapass.  However,  the  average  for  the  four  years 
at  each  of  the  three  higher  stations  at  Tryon  is  higher  than 
at  No.  1,  although  in  steadily  decreasing  amounts  from 
No.  2  upward. 

The  conditions  at  Tryon,  with  a  high  plateau  over¬ 
looking  the  Pacolet  valley,  are  ideal  for  the  development 
of  the  mountain  breeze  at  night,  and  an  examination  of 
the  trace  sheets  at  No.  1,  on  the  valley  floor,  shows  this 
to  be  the  case  during  periods  of  anticyclonic  weather. 
The  strength  of  the  breeze  is  either  aided  or  impeded 
according  to  the  direction  and  speed  of  the  general  air 
movement. 

The  increase  in  temperature  during  the  selected  May 
period  of  inversion  (Table  2a)  was  quite  marked  from 
the  base  to  No.  2  station,  380  feet  above  with  an  average 
excess  of  14.4°,  but,  of  course,  this  rate  of  increase  does 
not  compare  with  the  increase  at  the  lower  levels  of  the 
slope  at  Highlands,  Transon,  or  Mount  Airy.  During 
the  November  period  the  inversions  were  not  so  large  as 
those  found  in  the  spring,  and  this  was  largely  due  to 
the  prevalence  of  the  mountain  breeze  during  the  former 
period,  which  prevents  the  temperature  at  No.  1  from 
reaching  a  low  point. 

During  norm  conditions  at  Tryon  (Table  2a)  the  aver¬ 
age  rate  of  decrease  in  minimum  temperature  is  about 
normal  between  Nos.  1  and  2,  while  the  decrease  between 
Nos.  1  and  4  is  1.4°  for  each  300  feet,  or  slightly  in  excess 
of  the  normal  rate  in  this  region.  Between  Nos.  2  and 
3  there  is  a  decrease  at  the  rate  of  2.5°  for  300  feet.  It 
is  not  understood  why  there  should  be  the  great  difference 
in  minimum  temperature  between  these  two  stations 
located  only  a  short  distance  from  each  other,  and  it  is 
probable  that  a  part  of  the  difference  is  due  to  instru¬ 
mental  errors  that  were  not  detected  during  the  period 
of  the  observations,  although  every  precaution  was  taken 
to  check  the  readings  and  correct  all  errors. 

Wilkesboro  (Table  2). — This  group,  like  Mount  Airy, 
having  a  low  altitude,  with  the  slope  ranging  in  elevation 
from  1,240  feet  to  1,670  feet  above  sea  level,  also  has 
minimum  temperatures  relatively  high. 

No.  1  is  a  cold  station  during  inversion  weather  and, 
although  not  on  a  valley  floor,  is  located  on  a  bench  or 
nearly  level  portion  of  the  slope.  The  exposure  at  No.  2 
is  better,  and  that  station  is  free  from  frost  during 
critical  periods.  During  inversion  weather  the  differences 
between  Nos.  1,  2,  3,  and  4  are  greater  with  high  pressure 
north  of  the  station  than  when  it  is  to  the  south.  The 


THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 


barrier  of  the  Brushy  Mountains  cuts  off  any  flow  of  light 
southerly  wind  and  allows  the  cold  air  to  accumulate^on 
the  comparatively  level  portions  of  the  slope. 

Nos.  3  and  4  are  quite  warm,  No.  3  being  on  a  small 
knob  and  No.  4  on  the  crest  of  a  small  ridge,  averaging 
tor  the  four-year  period,  respectively,  3.5°  and  3.6°  above 
j These  figures  exceed  the  four-year  average 
differences  recorded  even  at  Bryson,  Globe,  and  Blantyre 
and  compare  with  those  at  Hendersonville  for  the  same 
period. 

During  the  selected  periods  of  inversion  (Table  2a) 
the  increase  in  temperature  with  elevation  at  Wilkesboro 
is  quite  pronounced,  although  not  so  marked  as  on  the 
west  slope  at  Mount  Airy.  The  effect  of  northerly  winds 
during  the  November  period  is  markedly  shown  in  the 
larg6  amounts  of  inversions,  Nos.  3  and  4  averaging  14° 
and  15.4°,  respectively,  higher  than  No.  1.  Wilkesboro 
is  the  only  point  in  the  research  where  the  inversions 
were  greater  in  the  November  than  in  the  May  period, 
as  is  evident  from  an  inspection  of  Table  2a.  The  range 
of  inversion  here  in  the  November  period  is  in  harmony 
with  the  four-year  average  differences  in  minimum 
temperature  and  even  exceeds  those  observed  at  Bryson, 
Globe,  and  Blantyre. 

The  difference  in  elevation  between  the  Wilkesboro 
stations  is  only  slight,  so  that  during  norm  conditions 
there  is  naturally  not  much  variation  in  temperature,  as 
shown  by  Table  2a. 

Variation  in  minimum  temperature  during  periods  of 
inversion  in  spring  and  autumn. — Figures  47  and  48 
strikingly  illustrate  the  variation  in  minimum  tempera¬ 
ture  in  the  region  as  a  whole  during  the  selected  periods 
of  inversion  in  spring  and  autumn,  the  data  for  which 
are  given  in  detail  in  Table  2a. 

In  both  May  and  November  periods  the  nights  were 
clear,  with  calm  air  or  light  south  to  southeast  winds  in 
the  former  and  light  to  gentle  northwest  winds  in  the 
latter. 

At  a  glance  one  may  determine  the  character  of  the 
exposure  of  the  stations  having  approximately  similar 
elevation,  or,  at  least,  whether  they  are  valley-floor  sta¬ 
tions  on  the  one  hand  or  slope  and  summit  stations  on 
the  other. 

For  instance,  note  the  high  temperature  during  both 
these  periods  at  Tryon  No.  2  on  a  slope  as  compared  with 
the  valley-floor  stations  having  approximately  the  same 
elevation,  and  especially  with  that  at  Gorge  No.  1,  the 
latter  registering  21.7°  lower  in  the  spring  period  and 
19.3°  lower  in  the  autumn  period  than  the  Tryon  station. 

Then  we  may  compare  the  summit  station,  Tryon  No. 
4,  with  the  cold  base  station  at  Blantyre,  where  we  find 
in  the  spring  period  a  difference  of  23.2°  and  in  the  autumn 
the  smaller  difference  of  14.5°. 

There  are  also  large  differences  apparent  in  the  two 
periods  between  the  summit  station  at  Gorge  and  the 
valley  floor  station  at  Asheville,  both  having  about  the 
same  elevation,  and  between  the  summit  station  at  Globe 
and  the  valley-floor  station  at  Cane  River. 

There  are  the  unusually  large  differences  between  the 
minima  on  the  valle}^  floor  in  the  Waldheim  orchard  at 
Highlands,  station  No.  3,  and  several  other  stations  with 
approximately  the  same  elevation,  the  base  station  at 
Highlands  in  practically  every  case  being  20°  or  more 
lower  than  any  of  the  slope  or  summit  stations.  In  the 
spring  period  the  difference  between  the  minimum  in 
the  Highlands  frost  pocket  and  the  summit  station  at 
Cane  River  was  23.4°  and  in  the  autumn  21.0°. 

The  figures  also  furnish  some  light  on  the  relative 
exposures  of  the  base  stations.  Thus,  compare  the  read¬ 


ings  at  the  base  station  at  Gorge  with  that  at  Mount 
Airy,  the  former  being  much  colder,  as  it  is  in  a  frost 
pocket. 

Compare  the  base  stations  at  Bryson,  Blantyre,  Hen¬ 
dersonville,  Ellijay,  and  Altapass,  the  first  two  named 
being  the  coldest  because  they  are  located  in  wide  frost 
pockets.  Ellijay  No.  1  is  not  so  cold,  because  free  radia¬ 
tion  on  that  valley  floor  is  obstructed  by  the  towering 
mountains  on  both  sides.  Station  No.  1  at  Altapass  is, 
of  course,  much  warmer,  because  of  its  location  on  a 
slope. 

The  valley-floor  characteristics  of  the  slope  stations, 
No.  2,  at  Gorge  and  Blantyre,  are  also  brought  out  by 
this  comparison,  the  minima  at  these  two  stations  aver¬ 
aging  much  lower  than  at  the  other  stations  on  slopes 
or  summits  having  approximately  the  same  elevation. 
In  fact,  Blantyre  No.  2  averages  lower  than  Asheville 
No.  1  during  inversions. 

It  is  also  evident  from  the  figures  that  the  No.  1 
stations  at  Blowing  Rock  and  Highlands  are  not  valley- 
floor  stations,  but  rather  located  on  slopes  where  the 
minima  during  inversions  are  quite  high. 

Moreover,  the  data  in  Figures  47  and  48  furnish  a  basis 
for  comparison  between  the  summit  stations.  Station 
No.  5  at  Gorge  and  No.  3  at  Globe,  with  their  relatively 
high  minima,  stand  out  as  rather  warm;  also  Cane  River 
summit  station,  No.  4. 

The  high  minima  at  the  summit  stations  of  Gorge  and 
Globe  are  in  strong  contrast  to  the  low  minima  at  the 
summit  station  at  Bryson  No.  3.  The  stations  in  the 
Bryson  group  differ  only  slightly  in  elevation,  and,  while 
marked  inversions  occur  there,  the  section  as  a  whole  is 
in  a  wide  frost  pocket  with  surrounding  mountains  at 
great  elevation.  The  center  of  the  thermal  belt  at  Bryson 
would  be  at  a  much  higher  elevation  were  the  slope  of 
greater  altitude. 

The  minima  are  shown  to  be  low  on  the  summit,  at 
Altapass,  station  No.  5,  because  of  the  great  surface 
area  surrounding  it  during  inversions,  as  compared  with 
other  summits  and  with  other  slopes  of  approximately 
the  same  or  even  higher  elevation.  Altapass  is  on  an 
elevated  plateau  on  the  main  Blue  Ridge  with  oppor¬ 
tunity  for  free  radiation  at  station  No.  5,  and  the  loss 
of  heat  through  radiation  from  this  large  mass  is  large 
as  compared  with  that  received  by  interchange  with  the 
free  air. 

The  differences  between  the  minima  at  this  summit 
station  in  the  selected  spring  and  autumn  periods  of 
inversion  and  the  other  summit  stations  of  higher  ele¬ 
vation,  such  as  Ellijay,  Cane  River,  Transon,  and  High¬ 
lands,  are  striking,  Altapass  registering  from  5°  to  7° 
lower,  although  normally,  because  of  lower  elevation 
alone,  it  should  read  higher.  The  knobs  upon  which 
these  other  summit  stations  are  located  being  small, 
partake  of  the  temperature  of  the  surrounding  warm 
tree  air.  The  effect  of  summit  area  upon  night  minima 
is  brought  out  strongly  in  this  comparison. 

The  summit  area  at  the  highest  station  at  Blowing 
Rock  is  also  considerable,  but  not  so  great  as  at  Altapass, 
and  we  find  here  that  during  the  selected  periods  of 
inversion  station  No.  5  at  Blowing  Rock  averages  about 
3°  lower  than  station  No.  5  at  Highlands. 

So  the  summit  station  at  Tryon  No  4  in  the  November 
period  has  a  low  minimum  as  compared  with  many  sum¬ 
mit  and  slope  stations  higher  up  during  the  prevalence 
of  light  northwest  winds,  when  the  effect  of  loss  of  heat 
through  radiation  from  the  high  plateau  is  pronounced, 
and  this  difference  exists  in  spite  of  the  fact  that  Tryon 
has  one  of  the  most  southerly  positions.  In  the  May 


30442—23 - 4 


44 


SUPPLEMENT  NO.  19. 


period,  with  prevailing  south  to  southeast  winds,  the 
temperature  on  the  Tryon  summit  was  not  so  low. 

Bate  of  increase  or  decrease  in  average  monthly  and 
annual  minimum  temperature  on  six  selected  long  slopes. — 
Table  2b  contains  a  comparison  of  the  mean  monthly 
and  annual  minimum  temperatures  for  the  lowest 
and  the  highest  stations  on  the  six  longest  slopes  having 
a  difference  in  elevation  of  1,000  feet  or  more,  after 
the  plan  of  Table  lb,  which  gives  a  comparison  of 
the  mean  maximum  temperature.  This  table  will  sup¬ 
plement  the  tables  of  other  minimum  temperature  data 
which  have  just  been  discussed. 

Because  of  the  influence  of  inversions  the  average 
minimum  temperature  for  the  four  years  is  lowest  at  the 
base  stations  of  five  of  the  six  slopes.  Altapass  is  the 
only  one  of  the  six  that  has  a  lower  average  minimum 
at  the  summit  than  at  its  No.  1  station,  and  this  con¬ 
dition  is  persistent  throughout  all  months.  However, 
if  Altapass  No.  1  were  located  on  a  valley  floor,  the 
observations  on  that  slope  might  show  much  the  same 
relation  as  those  noted  on  the  other  slopes,  with  the  base 
station  averaging  the  lower,  although  this  might  not  be 
so,  as  the  summit  at  Altapass,  because  of  the  great 
summit  area  surrounding,  has  comparatively  low  minima, 
as  we  have  already  seen. 

The  four-year  average  for  March  at  the  base  station  at 
Cane  River  is  slightly  higher  than  that  at  the  summit, 
and  this  relation  is  true  also  at  Tryon  from  June  to 
October,  inclusive.  At  the  latter  place  in  December 
there  is  no  difference  between  the  averages  at  the  base 
and  summit  stations,  nor  at  Ellijay  in  March;  other¬ 
wise  the  averages  at  the  base  stations  are  lower  than 


those  at  the  summit.  At  Tryon  the  small  increase  in 
average  minima  between  the  base  and  summit  is  not 
indicative  of  either  the  frequency  or  amount  of  inver¬ 
sion,  as  the  point  of  highest  minima  on  this  slope  lies 
between  the  two  at  an  unusually  low  altitude,  400  to 
500  feet  above  the  valley  floor. 

Of  all  these  selected  slopes  the  greatest  rate  of  increase 
in  annual  average  minimum  temperature  between  the 
base  and  summit  stations  is  at  Gorge,  1°  for  231  feet,  the 
average  minimum  at  No.  5  at  this  point  exceeding  that 
at  No.  1  by  4.5°.  The  rate  of  increase  in  minimum 
temperature  would  naturally  be  the  greatest  on  the 
slope  having  the  largest  inversions  for  the  least  difference 
in  altitude  between  base  and  summit,  and  this  relation, 
as  brought  out  later  in  the  discussion  of  "Inversions,” 
is  most  marked  at  Gorge.  The  slopes  at  Cane  River  and 
Globe  have  rates  of  increase  amounting  to  1°  for  355 
and  357  feet,  respectively,  while  Ellijay,  with  about  the 
same  difference  in  average  minima  between  its  summit 
and  base  stations  as  Cane  River  and  Globe,  has  actually 
a  smaller  rate  of  increase,  doubtless  because  of  the 
greater  length  of  its  slope. 

Excepting  Altapass,  the  greatest  average  monthly  rate 
of  increase  on  all  the  slopes  occurs  in  the  spring  and 
autumn,  usually  in  May  and  November,  when  inversions 
are  most  pronounced.  Even  at  Altapass  the  tendency 
to  less  pronounced  norms  in  May,  October,  and  Novem¬ 
ber  is  shown  by  the  rate  of  decrease  in  average  minima 
during  those  months. 

This  table  brings  out  strongly  the  great  preponderance 
of  inversion  over  norm  conditions. 


Table  2b. —  Monthly  and  annual  average  minimum  temperatures  on  the  six  long  slopes,  shoiving  rate  of  increase  or  decrease  with  elevation,  1918-1916. 

[The  slopes  selected  for  this  comparison  have  a  difference  in  elevation  of  1,000  feet  or  more  between  the  base  and  summit  station.  The  difference  in  temperature  between  the 
base  and  summit  stations  on  each  slope  is  given,  as  well  as  the  difference  in  feet  for  each  degree  difference  in  temperature.] 


Slopes  and  stations. 


Altapass  No.  1 . 

Altapass  No.  5 . 

Difference . 

Feet  for  1*  difference. 

Cane  River  No.  1 _ 

Cane  River  No.  4 _ 

Difference . 

Feet  for  1°  difference. 

Ellijay  No.  1 . 

Ellijay  No.  5 . 

Difference . 

Feet  for  1°  difference. 

Globe  No.  1 . 

Globe  No.  3 . 

Difference . 

Feet  for  1°  difference. 

Gorge  No.  1 . 

Gorge  No.  5 . 

Difference . 

Feet  for  1°  difference 

Tryon  No.  1 . 

Tryon  No.  4 . 

Difference . 

Feet  for  1°  difference 


Elevation.1 


Base.  Summit. 


Feet. 

2,230 


Feet. 

”i,'666' 


2,650 


1,100 


2,240 


1,760 


1,625 


1,000 


1,400 


1,040 


950 


1, 100 


Janu¬ 

ary. 

Febru¬ 

ary. 

March. 

April. 

May. 

June. 

July. 

August. 

Sep¬ 

tember 

Octo¬ 

ber. 

Novem¬ 

ber. 

Decem¬ 

ber. 

Annual . 

31.1 

29.1 

31.5 

44.2 

52.8 

58.4 

60.5 

61.3 

54.0 

46.3 

36.6 

29.8 

44.8 

29.1 

27.0 

28.8 

42.1 

51.0 

55.8 

60.2 

59.5 

52.5 

45.2 

35.4 

27.4 

42.9 

-2.0 

-2.1 

-2.7 

-2.1 

-1.8 

-2.6 

-2.3 

-1.8 

-1.5 

-1. 1 

-1.2 

-2.4 

-1.9 

500 

476 

370 

476 

556 

385 

435 

556 

667 

909 

833 

417 

526 

26.4 

25.7 

27.2 

37.6 

46.6 

53.9 

58.1 

58.0 

49.6 

40.4 

28.5 

24.8 

39.7 

28.8 

26.9 

27.1 

41.0 

51.3 

56.7 

60.2 

59.6 

53.1 

45.3 

36.3 

27.2 

42.8 

+2.4 

+1.2 

-0.1 

+3.4 

+4.7 

+2.8 

+2.1 

+  1.6 

+3.5 

+4.9 

+7.8 

+2.4 

+3.1 

458 

917 

1  11,000 

324 

234 

393 

524 

688 

314 

224 

141 

458 

355 

30.2 

27.7 

28.6 

39.7 

48.2 

54.7 

58.8 

58.4 

51.1 

42.5 

31.1 

27.4 

41.6 

32.6 

29.6 

28. 6 

44.2 

54.0 

58.4 

60.9 

60.0 

54.7 

48. 1 

37.7 

28.6 

44.9 

+  2.4 

+  1.9 

0 

+4.5 

+5.8 

+3.7 

+2.1 

+1.6 

+  3.6 

+5.6 

+6.6 

+  1.2 

+3.3 

733 

926 

0 

391 

303 

476 

838 

1, 100 

489 

314 

267 

1,467 

533 

31.8 

29.0 

32.4 

41.9 

51.1 

58.0 

62.0 

61.6 

54.6 

46.5 

34.6 

29.2 

44.4 

33.6 

30.4 

33.5 

46.0 

55.9 

61.2 

64.6 

63.5 

57.2 

49.7 

39.8 

30.8 

47.2 

+  1.8 

+  1.4 

+  1.4 

+4.1 

+  4.8 

+3.2 

+2.6 

+  1.9 

+  2.6 

+3.2 

+5.2 

+1.6 

+2.8 

556 

714 

714 

244 

208 

312 

385 

526 

385 

312 

192 

625 

357 

30.8 

28.1 

32.3 

40.5 

49.3 

56.8 

61.1 

61.0 

53.9 

45.2 

32.8 

27.9 

43.3 

33.5 

30.9 

34.4 

46.9 

57.0 

61.4 

64.9 

63.7 

57.7 

49.9 

41.1 

32.0 

47.8 

+2.7 

+  2.8 

+  2.1 

+  6.4 

+7.7 

+  4.6 

+3.8 

+2.7 

+3.8 

+4.7 

+8.3 

+4.1 

+4.5 

385 

371 

495 

162 

135 

226 

274 

385 

274 

221 

125 

254 

231 

34.7 

32.3 

35.9 

44.7 

54.8 

63.0 

66.7 

66.3 

58.5 

50.6 

37.3 

32.8 

48.1 

35.8 

33.3 

36.2 

47.5 

56.9 

61.9 

65.0 

64.4 

58.0 

47.7 

40.6 

32.8 

48.8 

+  1.1 

+  1.0 

+0.3 

+  2.8 

+2.1 

-1.1 

-1.7 

-1.9 

-0.5 

-2.9 

+3.3 

0 

+0.7 

1, 000 

1, 100 

3,667 

393 

524 

1,000 

647 

! 

579 

2,200 

379 

333 

0 

1,571 

1  Base  station  above  sea  level;  summit  above  base. 

1  The  datum  ‘  Feet  for  1  difference”  obviously  fails  of  any  physical  significance  when  the  temperature  differences  between  slope  stations  are  quite  small. — Ei>. 


THERMAL  BELTS  AND  FRUIT 


Monthly  and  average  annual  minima  at  the  two  stations 
having,  respectively,  the  highest  and  lowest  elevations.— In 

Iowp^uV1}6  t6'10  nxTllma  at  the  station  having  the 
lowest  altitude  Tryon  No.  1,  a  valley-floor  station,  with 

the  most  elevated  station,  Highlands  No.  5,  located  a 
short  distance  below  the  summit  of  Dog  Mountain,  with 
a  difference  m  elevation  of  3,125  feet  (Table  2c),  we  find 
that  the  Highlands  station  averages  the  lower  throughout 
all  themonths  of  the  year,  with  an  average  difference  of 
5.6  ,  the  greatest  difference,  10.5°,  being  in  March,  when 
norms  are  most  frequent,  and  the  least,  0.5°,  in  No¬ 
vember,  a  month  marked  by  frequent  inversions.  The 
average  decrease  for  the  entire  four-year  period  amounts 
to  1  tor  558  feet. 


Table  2c  Average  monthly  and  annual  minimum  temperatures  at 
the  two  stations  having,  respectively,  the  highest  and  lowest  elevations, 
showing  rate  of  decrease  with  elevation ,  1913-1916. 


Eleva¬ 

tion. 

Jan¬ 

uary. 

Feb¬ 

ruary. 

March. 

April. 

May. 

June. 

Tryon  No.  1 . 

Highlands  No.  5 . 

Difference . 

F eet  for  1  °  difference .... 

Feet. 

950 

4,075 

34.7 

28.6 

-6.1 

512 

32.3 

25.7 

-6.6 

473 

35.9 

25.4 

-10.5 

298 

44.7 

41.5 

-3.2 

977 

54.8 

51.4 

-3.4 

919 

63. 0 
56.5 
-6.5 

481 

Eleva¬ 

tion. 

July. 

August. 

Sep¬ 

tember. 

Octo¬ 

ber. 

Novem¬ 

ber. 

Decem¬ 

ber. 

Annual. 

Tryon  No.  1 . 

Highlands  No.  5 . . . 

Difference . 

Feet  for  1°  differ¬ 
ence  . 

Feet. 

950 

4,075 

66.7 

59.8 
-6.9 

453 

66.3 

58.7 

-7.6 

411 

58.5 

52.6 
-5.9 

530 

50.6 

46.0 

-4.6 

679 

37.3 

36.8 

-0.5 

6,250 

32.3 

28.6 

-3.7 

840 

48.1 

42.5 

-56 

558 

NORMS. 

The  graph,  Figure  49,  illustrates  the  variation  in  aver¬ 
age  minimum  temperature  on  the  selected  dates  in  Jan¬ 
uary,  February,  and  March,  1916,  during  norm  condi¬ 
tions,  the  data  for  which  are  given  in  detail  in  Table  2a. 

In  considering  this  graph  we  should  make  due  allow¬ 
ance  for  latitude,  and  the  figures  might  be  reduced  to 
the  parallel  of  35°,  approximately  the  position  of  High¬ 
lands,  by  using  corrections,  the  largest  of  which  would  be 
3°  for  Mount  Airy,  located  in  the  extreme  north,  the 
correction  for  the  other  stations  lying  between  that 
amount  and  zero.  The  lowest  average  minimum  during 
this  period  is  8.8°,  at  Blowing  Rock  No.  5,  one  of  the 
most  elevated  stations  and  one  of  the  most  northerly, 
while  the  other  summit  stations  having  a  greater  altitude, 
Ellijay  and  Highlands,  have  considerably  higher  minima, 
11.5°  and  10.6°,  respectively;  but  if  due  correction  were 
made  for  difference  in  latitude  the  excesses  at  the  more 
southerly  stations,  Ellijay  and  Highlands,  would  be 
largely  offset. 

On  the  selected  nights  there  seems  to  be  a  general  de¬ 
crease  in  temperature  with  elevation  from  the  lowest 
station  at  Tryon  to  these  high-level  stations,  but  this 
decrease  is  not  uniform,  mainly  because  of  difference  in 
latitude  and  in  some  cases  because  of  difference  in  topo¬ 
graphy  and  slight  influences  of  inversion.  In  this  respect 
Figure  49  furnishes  data  in  strong  contrast  with  Figures 
47  and  48,  which  present  mean  minimum  temperatures 
for  the  various  stations  during  the  two  selected  periods 
of  inversion  weather.  While  topography  has  little 
effect  upon  the  minimum  temperature  during  norm  con¬ 
ditions  as  compared  with  inversion,  its  influence  is  never¬ 
theless  apparent.  We  find  by  referring  to  Figure  49, 
that  almost  invariably,  of  the  stations  having  the  same 
elevation  base  stations  register  the  lowest  and  upper 


GROWING  IN  NORTH  CAROLINA.  45 

stations  the  highest  minima.  There  is  no  question  that 
during  clear  weather  at  night,  even  with  strong  winds 
Irom  the  northwest,  surface  area  is  a  factor  in  increasing 

le  loss  of  heat  through  radiation  from  the  ground,  pro- 
vided  it  is  colder  than  the  free  air,  and  this  study  shows 
ttiat  m  the  mountain  region  there  is  always  a  tendency 
toward  inversion,  with  a  consequent  lowering  of  tem¬ 
perature  on  the  valley  floors.  This  effect,  however,  was 
largely  neutralized  on  these  dates  selected,  as  the  weather 
was  mostly  windy,  and  thus  the  average  decrease  in 
minimum  with  elevation  in  the  region  approximates 
closely  the  adiabatic  rate. 

Comparing  the  mean  minima  for  the  days  selected  at 
the  lowest  and  highest  stations  in  the  region— Tryon 
No.  1,  a  base  station  with  an  elevation  of  950  feet  above 
sea  level  and  an  average  minimum  of  25.7°,  and  Hio-h- 
lands  No.  5,  a  summit  station  with  an  elevation  of  4,075 
feet  and  an  average  minimum  of  10.6° — we  find  a  differ¬ 
ence  m  temperature  of  15.1°,  or  a  rate  of  decrease  with 
elevation  of  1.4°  for  300  feet. 

Moreover,  the  mean  minimum  for  the  whole  region 
shows  an  average  decrease  in  temperature  for  elevation 
of  about  1.5°  for  each  300  feet  of  ascent.  Individual 
dates  at  Ellijay  show  rates  as  much  as  1.9°  per  300  feet, 
which  are  _  superadiabatic.  With  falling  temperature 
over  an  entire  slope,  as  in  the  approach  of  a  general  cold 
wave,  it  is  evident  that  there  is  a  strong  overrunning  at  the 
more  elevated  stations,  and  the  vertical  temperature 
gradient  then  becomes  strongly  superadiabatic. 

At  Bryson  and  Ellijay,  which  are  in  the  extreme 
western  part  of  the  region,  clear  weather  prevailed  in  the 
early  morning  on  two,  and  possibly  three,  of  the  dates 
used  in  the  table,  allowing  a  slight  inversion  between 
the  two  lower  stations,  which  reduced  somewhat  the 
average  differences  on  these  slopes.  Thus  at  Ellijay  we 
have  an  average  difference  of  only  0.6°  for  the  first  300 
feet,  compared  with  the  rate  of  1.2°  per  300  feet  for  the 
entire  slope.  On  the  Altapass  slope  during  this  period 
the  rate  of  decrease  was  about  1.5°  for  each  300  feet  of 
elevation,  1.4°  at  Tryon,  and  1.5°  at  Cane  River.  The 
norm  condition  was  ideal  at  Globe  on  all  the  dates 
selected,  and  here  we  find  an  average  decrease  of  1.7° 
for  each  300  feet. 

In  comparing  the  Waldheim  orchard  stations,  Nos. 
3,  4,  and  5,  with  the  Satulah  orchard,  stations  Nos.  1  and 
2  at  Highlands,  the  protective  influence  of  Mount  Satulah 
seems  to  be  evidenced  by  the  higher  temperature  in  the 
latter. 

At  Asheville  stations  Nos.  2  and  3,  which  face  the  full 
force  of  the  northerly  winds,  seem  invariably  to  have  a 
lower  minimum  temperature  during  norm  conditions 
than  Nos.  2a  and  3a,  which  are  protected  somewhat  by 
a  steep  ridge  running  east  and  west.  The  cold  air 
evidently  sweeps  over  the  ridge,  striking  Nos.  2  and  3 
directly  and  reaching  the  other  stations  only  by  a  back 
flow  or  eddy.  Thus  with  a  lowering  temperature  there 
is  a  continual  delay  of  the  minimum  temperature  at 
Nos.  2a  and  3a,  until  finally,  after  daybreak,  the  temper¬ 
ature  begins  to  rise  at  all  stations,  although  much  earlier 
at  Nos.  2a  and  3a,  if  the  sun  is  shining. 

Under  norm  conditions  we  would  expect  the  tempera¬ 
ture  decrease  to  be  approximately  normal  because  the 
air  is  relatively  dry  and  at  the  various  elevations  is  mixed 
and  in  equilibrium.  Ordinarily  during  a  fall  in  temper¬ 
ature  the  thermograph  traces  on  any  long  slope  are 
found  in  parallel  lines,  or  approximately  so,  and  this 
condition  is  well  illustrated  by  Figure  69,  which  shows 
the  thermograph  traces  during  a  typical  cold  wove, 
March  2-4,  1916,  on  the  slopes  of  Ellijay  and  Altapass. 


46 


SUPPLEMENT  NO.  19. 


The  effect  of  decrease  in  temperature  with  elevation 
is  strikingly  shown  in  Figure  49,  and  this  is  a  most  impor¬ 
tant  factor  in  the  growing  of  fruit  in  the  Carolina  moun¬ 
tain  region.  While  frost  may  at  times  during  inversion 
conditions  be  damaging  on  valley  floors,  it  is  the  cold  of 
elevation  during  norm  conditions  that  causes  the  greatest 
injury.  We  will  see  later  as  we  proceed  in  the  discussion 
that  the  length  of  the  growing  season  depends  largely 
upon  the  altitude,  and  reasons  will  be  given  why  successful 
fruit  growing  is  not  found  at  the  higher  levels  of  this 
region. 


ABSOLUTE  MAXIMUM  AND  ABSOLUTE  MINIMUM  TEMPER¬ 
ATURES. 

In  connection  with  fruit  growing,  the  absolute  maxima 
and  absolute  minima  doubtless  are  just  as  important  as 
the  average  maxima  and  average  minima,  the  extremes 
indicating  the  limits  wi thin  which  the  temperatures  lie, 
operating  toward  safety  or  injury.  The  absolute  minima 
are  especially  important.  Table  3  gives  the  absolute 
maxima,  the  absolute  minima,  and  the  absolute  ranges 
in  temperature  at  the  different  stations  for  the  four  years 
of  the  research.  This  table  supplements  previous  ones 
and  contains  material  that  should  be  useful  for  study 
purposes.  It  hardly  seems  advisable  to  go  into  a  dis¬ 
cussion  of  the  data  in  great  detail,  but  reference  will  be 
made  to  the  more  important  features. 

The  highest  absolute  maximum  in  the  entire  region, 
103°,  occurred  July  19,  1913,  at  the  Tryon  lower-level 
stations,  Nos.  1  and  2,  and  the  other  stations  at  which 
100°  was  reached  or  exceeded,  Gorge  Nos.  1  and  5,  Mount 
Airy  No.  1,  Tryon  Nos.  3  and  4,  and  Wilkesboro  Nos.  1, 
2,  3,  and  4,  were  in  no  case  above  the  2,100-foot  level, 
except  Gorge  No.  5,  which  has  an  elevation  of  2,440  feet. 
Maxima  as  high  as  100°  were  registered  in  only  two  of 
the  four  years,  1913  and  1914.  There  was  a  general  de¬ 
crease  from  the  100°  mark  downward  through  the  90’s, 
every  station  registering  a  maximum  of  90°  or  over  in 
one  or  more  summers,  except  Nos.  2,  3,  4,  and  5  at  Blow¬ 
ing  Rock  and  Nos.  3,  4,  and  5  at  Highlands,  all  above 
the  3,500-foot  level  in  the  two  most  elevated  groups.  Of 
these  seven  stations,  Blowing  Rock  Nos.  2,  3,  and  5  and 
Highlands  Nos.  3  and  4  had  a  four-year  absolute  maxi¬ 
mum  of  88°,  the  other  two  having  one  of  89°.  Thus  we 
have  for  the  four-year  period  an  extreme  variation  of 
15°,  from  103°  to  88°,  in  the  absolute  maxima  in  this 


region,  with  stations  ranging  in  elevation  from  950  feet 
at  Tryon  to  4,075  feet  at  Highlands.  At  the  latter  ele¬ 
vation,  Highlands  No.  5,  however,  the  absolute  maxi¬ 
mum  was  89°,  1°  in  excess  of  the  lowest  absolute  maxi¬ 
mum,  88°,  registered  at  certain  stations  of  lower  altitude 
at  both  Highlands  and  Blowing  Rock  named  above. 

As  already  stated,  a  maximum  of  100°  in  this  mountain 
region  is  not  reached  every  year  by  any  means,  even  at 
Tryon,  where  the  highest  readings  in  1915  and  1916  were 
99°  and  97°,  respectively.  Moreover,  90°  is  not  regis¬ 
tered  each  year  on  an  average  at  any  one  of  the  Blowing 
Rock  or  Highlands  stations,  their  highest  annual  read¬ 
ings  usually  being  considerably  below  that  mark.  In 
1916  the  absolute  maxima  at  Blowing  Rock  ranged  from 
85°  to  81°  and  at  Highlands  from  87°  to  85°,  the  low 
reading  of  81°  at  Blowing  Rock  being  registered  on  June 
30,  at  station  No.  5,  3,930  feet  above  sea  level.  In  spite 
of  the  elevation,  81°  seems  to  be  an  exceedingly  low  max¬ 
imum  temperature  for  an  entire  year.  It  is  the  lowest 
summer  maximum  registered  during  the  period  of  the 
research.  Both  Blowing  Rock  and  Highlands  are  located 
on  elevated  plateaus,  the  former  close  to  the  Tennessee 
border  on  the  north  and  the  latter  only  a  few  miles  from 
the  Georgia  border  on  the  south,  as  shown  by  the  relief 
map.  At  Highlands  ideal  summer-resort  weather  pre¬ 
vails  during  the  heated  season,  though  its  latitude  is  only 
about  35°  N.  The  summer  temperature  is  even  lower 
at  Blowing  Rock,  located  far  to  the  north. 

Station  No.  3  at  Highlands,  with  an  elevation  of  3,675 
feet,  has  the  lowest  minimum  during  the  four-year  period, 

—  7°  on  December  15,  1914,  and  in  no  other  year  did  the 
temperature  at  any  one  of  the  Highlands  stations  fall 
below  zero.  No.  3,  at  which  this  low  minimum  occurred, 
is  in  the  frost  pocket  so  often  referred  to  in  this  discussion, 
where  the  lowest  average  minima  in  the  entire  region  are 
also  observed  (see  Table  2).  Highlands  Nos.  4  and  5 
recorded  a  minimum  of  —2°  on  March  2,  1914.  The 
absolute  minimum  at  Blowing  Rock  was  —5°  at  No.  5, 
3,930  feet  above  sea  level,  on  December  15,  1914,  the 
same  date  on  which  the  absolute  minimum  of  —7°  was 
registered  at  Highlands  No.  3. 

The  lowest  minimum,  considering  the  elevation,  was 

—  6°  at  Blantyre  No.  1,  elevation  2,090  feet,  observed  also 
on  December  15,  1914.  It  has  been  stated  previously 
that  the  average  minima  also  at  Blantyre  are  relatively 
low,  because  of  the  low  night  temperatures  there  during 
nights  of  inversion.  The  valley  of  the  French  Broad, 
where  Blantyre  is  located,  is  rather  wide  with  gentle 
grade,  and  this  condition,  together  with  the  surrounding 
mountains  in  the  distance,  forms  an  extensive  frost 
pocket,  favoring  the  occurrence  of  abnormally  low 
minima  during  inversion  conditions. 

The  Bryson  region  is  somewhat  similar  topographi¬ 
cally,  and  the  average  minima,  at  both  places  are  low 
during  inversion  conditions,  but,  nevertheless,  at  none 
of  the  Bryson  stations  was  an  absolute  minimum  of 
zero  recorded  during  the  entire  four-year  period,  the 
lowest  being  1°  above  zero  on  December  15,  1914,  at  the 
summit  station,  No.  3. 

The  Tryon  stations,  at  which  high  maxima  are 
observed,  have  relatively  high  minima  also,  the  lowest, 
7°,  being  recorded  at  both  Nos.  1  and  4,  at  the  former, 
December  20,  1916,  and  at  the  latter,  December  15,  1914. 
Nos.  2  and  3  have  minima  of  12°  and  10°,  respectively, 
and  these  are  the  highest  absolute  minima  noted  in  the 
entire  region  during  the  period  of  the  research. 

So  the  highest  absolute  maxima  and  minima  are 
registered  at  stations  in  the  Tryon  group,  the  lowest  in 
elevation,  just  as  the  lowest  absolute  maxima  and 


THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 


47 


minima  are  observed  in  the  most  elevated  groups,  Blow¬ 
ing  Rock  and  Highlands.  While  the  highest  maxima 
occur  in  July  and  August,  the  lowest  minima  during  the 
four-year  period  do  not,  as  a  rule,  occur  in  January  and 
February,  as  would  ordinarily  be  expected.  The  lowest 
mark  was  reached  at  most  of  the  stations  diming  the  cold 
spell  from  December  14-16,  1914.  In  fact,  there  is  not 
a.  single  group  in  which  the  absolute  minimum  is  not 
registered  at  least  at  one  station  during  that  period.  At 
the  two  upper  stations  at  Ellijay,  Nos.  4  and  5,  and  at 
Highlands,  Nos.  1,  2,  4,  and  5,  the  lowest  temperature 
was  recorded  March  2,  1914,  and  at  Blowing  Rock  Nos. 
3  and  4,  Mount  Airy  No.  1,  and  Wilkesboro  No.  2,  on 
January  18,  1916. 

At  no  station  was  the  absolute  minimum  registered  in 
the  month  of  February,  although  the  average  minima  at 
all  stations  were  considerably  lower  in  February  than  in 
January.  The  same  may  be  said  regarding  the  maxima, 
but  this  is  because  there  were  two  warm  Januaries— 1913 
amd  1916 — and  not  because  January  is  normally  warmer 
than  February. 

The  figures  that  impress  one  most  in  this  discussion 
are  not  the  absolute  maxima,  but  rather  the  absolute 
minima.  The  absolute  maxima  are  usually  about 
what  should  be  expected  when  the  elevation  of  the  region 
is  considered,  but  one  is  rather  surprised  that  the  absolute 
minima  are  not  lower  and  the  winter  cold  is  not  more 
severe.  In  fact,  the  minima  are  relatively  high  during 
the  colder  months  of  the  year,  doubtless  because  in  the 
winter  there  occur  frequent  periods  of  precipitation 
with  high  relative  humidity  and  considerable  cloudiness. 
The  area  of  high  pressure  off  the  Carolina  coast  during 
that  season  is  ordinarily  not  persistent,  and  inversions 
of  temperature  are  infrequent.  Consequently  low  min¬ 
ima  are  due  then  almost  entirely  to  the  cold  brought 
from  the  regions  farther  west,  but  the  cold  waves  in 
their  eastward  and  southeastward  course  moderate 
steadily;  the  highs  passing  quickly  across  the  region, 
followed  usually  by  an  immediate  rise  in  temperature. 
Thus  the  minima  An  the  winter  occur  nearly  always 
under  warm  conditions  and  not  in  periods  of  inversion. 

Both  the  absolute  and  average  maxima,  as  well  as  the 
absolute  and  average  minima,  in  the  mountain  region 
are  comparatively  high  during  the  colder  months,  and 
periods  of  high  temperature  often  prevail  sufficiently 
long  to  promote  plant  growth. 

The  minimum  temperatures  during  the  summer  months 
as  compared  with  the  winter  minima  are  quite  low, 
especially  at  the  base  stations.  At  the  five  Blowing 
Rock  stations  during  the  four-year  period  the  minima 
in  the  month  of  June  ranged  from  33  to  38  ,  m  July 
from  39°  to  47°,  and  in  August  from  44  to  53  .  At 
the  five  Highlands  stations  the  minima  in  June  ranged 
from  32°  to  39°,  and  in  July  and  August  from  36  to 
52°  and  from  36°  to  51°,  respectively.  The  lowest 
June  minimum  at  Highlands,  32°,  was  rcAs,t®re{ni  ^ 
No.  3  on  June  10,  1916,  and  also  on  June  13  and  14,  1913, 
this  being  the  base  station  of  the  Waldheim  orchard, 
called  the  frost  pocket,  while  the  June  minimum  of  33 
was  recorded  at  Blowing  Rock  No.  3,  the  base  station 
of  the  Flat  Top  orchard,  June  11,  1913.  On  June  13 
and  14,  1913,  the  dates  on  which  minima  of  3^  weie 
recorded  at  Highlands  No.  3,  the  readings  at  Blowing 
Rock  No.  3  were,  respectively,  39  and  58  .  The 
remarkable  difference  of  26°  on  the  14th  between  the 
two  No.  3  stations  at  Highlands  and  Blowing  Rock  was 
due  entirely  to  the  influence  of  the  mountain  breeze 
at  Blowing  Rock,  which  prevented  the  temperature  at 
its  base  station  from  falling  to  a  low  point. 


No  mountain  breeze  is  ever  observed  at  Highlands 
No.  3  station,  which  is  situated  in  a  slight  depression 
with  no  outlet  at  the  base  of  a  slope  surmounted  by  a 
small  knob  and  surrounded  by  timber  on  the  other 
sides,  with  comparatively  level  country  beyond,  so  that 
there  is  no  opportunity  for  the  development  of  a  moun¬ 
tain  breeze  in  that  locality.  However,  the  plateau  at 
Blowing  Rock,  on  which  the  summit  station,  No.  5, 
stands,  has  considerable  surface  area,  and  there  is  an 
outlet  to  the  southeast  and  south  from  the  valley  floor 
where  No.  3  is  located,  with  a  steep  descent  beyond, 
the  position  being  especially  favorable  for  a  descending 
breeze  when  the  wind  is  from  the  north.  These  varia¬ 
tions  in  topographical  conditions  are  often  responsible 
for  great  differences  in  minimum  temperature  between 
the  two  places,  and  while  the  Blowing  Rock  station 
usually  has  low  minima  during  nights  of  inversion  the 
nocturnal  fall  in  temperature  is  often  retarded  because 
of  the  breeze  down  the  slope  from  Flat  Top. 

During  the  spring  rather  low  minima  are  observed 
at  Transon,  Blowing  Rock,  and  Highlands,  the  more 
elevated  places.  In  April  the  absolute  minima  are  far 
below  freezing.  Moreover,  in  May,  at  Transon  station 
No.  1,  a  minimum  of  25°  was  registered  in  1913  on  the 
11th.  Also  on  the  same  date  the  absolute  May  mini¬ 
mum  of  23°  was  registered  at  Blowing  Rock  No.  3  and 
one  of  27°  at  Highlands  No.  3  on  May  10,  1914.  Other 
places  having  minima  below  freezing  during  May  are 
Gorge  No.  2,  with  a  record  of  29°  May  11,  1913;  Cane 
River,  on  the  same  date,  with  a  record  of  30°  at  station 
No.  1;  and  both  Bryson  and  Blantyre  when  31°  was 
registered  at  the  base  stations  on  May  12,  1913,  and 
May  19  and  20,  1914,  respectively.  All  these  low 
minima  were  registered  at  the  stations  that  have  been 
shown  to  be  notably  cold  during  inversion  conditions 
and  where  the  average  annual  and  monthly  minima  are 
low. 

Transon  No.  1  and  Highlands  No.  3  are  the  only 
stations  where  freezing  temperature  was  observed  during 
any  June  in  the  four-year  period.  A  minimum  of 
31°  was  registered  at  the  former  on  June  11,  1913, 
while  readings  of  32°  were  registered  at  Highlands  on 
three  days  in  June  during  the  three-year  period.  The 
temperature  at  the  colder  station  at  Blowing  Rock, 
No.  3,  did  not  fall  quite  to  freezing  in  June,  probably 
because  of  the  influence  of  the  nocturnal  breeze  down 
the  slope. 

Comparatively  low  temperatures  are  registered  at 
these  three  places,  not  only  in  the  spring  and  summer, 
but  also  in  the  autumn.  In  practically  every  September 
the  temperature  falls  to  freezing  or  below  at  stations 
No.  3  at  both  Blowing  Rock  and  Highlands  and  at  No.  1 
at  Transon,  and  25°  was  registered  at  the  Highlands 
station  on  September  23,  1913.  The  lowest  at  Blowing 
Rock  was  30°  on  the  same  date.  . 

The  lowest  temperatures  registered  in  October  in  the 
four-year  research  were  12°  at  Highlands  and  19  at 
Blowing  Rock  in  1914  on  the  28th.  These  represent 
of  course,  the  conditions  in  the  frost  pockets  at  both 
places.  The  autumn  minima  at  the  other  stations  on 
these  two  slopes  are  considerably  higher,  especially  at 
Highlands.  For  instance,  the  lowest  temperature  in 
September  at  any  slope  station  at  Highlands  during  the 
four-year  period  was  35°  and  in  October  -0  .  In  anj 
case,  the  temperatures  in  the  spring  and  autumn  are 
usually  sufficiently  low  at  these  higher  altitudes 
limit  the  growing  season  to  a  period  too  short  for  t 
satisfactory  maturing  of  fruit. 


48 


SUPPLEMENT  NO.  19. 


At  Bryson  and  Blantyre,  also,  low  minima  are  ob¬ 
served  in  the  autumn,  freezing  temperature  usually 
occurring  at  the  base  stations  in  Doth  places  in  Septem¬ 
ber.  During  the  four-year  period  the  lowest  minimum 
in  this  month  was  31°  at  Blantyre  and  32°  at  Bryson. 
In  October,  moreover,  the  minima  at  these  two  places  are 
even  lower  than  those  at  Blowing  Rock,  but  not  so  low 
as  those  in  the  frost  pocket  at  Highlands. 

Tryon,  because  of  its  low  altitude,  does  not  seem  to 
experience  any  critical  temperatures  during  September, 
and  it  is  not  until  late  in  October,  after  harvesting  of  the 
fruit,  that  the  freezing  point  is  reached.  In  October 
minima  considerably  below  freezing  occur  throughout  the 
whole  mountain  region  with  the  exception  of  Tryon,  the 
absolute  minima  that  month  at  the  four  stations  dur¬ 
ing  the  four  years  of  the  research  being  only  slightly 
below  freezing. 

The  lowest  minima,  of  course,  are  at  the  bases  of  the 
respective  slopes,  while  the  orchards,  as  a  rule,  are  on 
the  slopes  above,  where  much  higher  minima  are  observed 
during  frosty  nights. 

One  is  impressed  with  the  low  minima  in  these  moun¬ 
tain  sections  during  the  spring,  summer,  and  autumn 
months,  especially  at  the  higher  levels.  Freezing  tem¬ 
perature  is  quite  common  during  the  month  of  April  and 
at  the  higher  elevations  and  in  frost  pockets  in  May,  and 


occasionally  even  in  June,  while  in  the  summer  months 
temperatures  below  40°  occur  frequently  in  the  colder 
places.  In  the  autumn  in  the  more  elevated  sections 
freezing  temperatures  invariably  occur  during  the  latter 
part  of  September,  and  by  October  minima  below  freez¬ 
ing  are  observed  in  practically  all  sections  of  the  region. 
On  the  other  hand,  relatively  high  maxima,  as  a  rule, 
are  observed  for  protracted  periods  during  the  winter 
and  early  spring,  as  high  as  60°  to  70°  or  more  in  January 
and  February  and  70°  to  80°  in  March.  These  unusual 
conditions  result  in  the  early  opening  of  buds  and  are 
often  followed  by  damaging  temperatures.  This  feature 
of  the  temperature  conditions  in  the  mountain  region 
will  be  discussed  in  extenso  later  in  connection  with  the 
discussion  of  "Hour-degrees  of  frost,”  the  occurrence  of 
frost  and  freezing  temperatures,  and  the  length  of  the 
growing  season. 

The  absolute  maxima  and  absolute  minima  in  each 
group  occur,  as  a  rule,  at  the  stations  where  the  highest 
average  maxima  and  lowest  average  minima,  respec¬ 
tively,  are  recorded,  and  in  the  large  majority  of  cases 
the  absolute  maxima,  the  highest  average  maxima,  the 
absolute  minima,  and  the  lowest  average  minima  are 
observed  at  the  base  stations.  Absolute  minima  recorded 
at  the  summit  occur  during  norm  conditions  and  those 
at  the  base  stations  during  nights  of  inversion 


Table  3. — Annual  maximum  and  minimum  temperatures  and  range  for  the  years  of  observation  (on  the  left )  and  absolute  maximum  and  minimum  for 

the  period  (on  the  right). 

[The  differences  between  the  averages  at  the  base  station  and  those  of  the  respective  slope  stations  may  be  seen  by  simple  inspection.] 


Principal  and  slope  stations;  elevation  of 
base  stations  above  mean  sea  level 
(feet). 

Height 

of 

slope 

stations 

above 

base 

(feet). 

1913 

1914 

1915 

1916 

l 

H 

c8 

S 

5 

© 

to 

fl 

a 

8 

a 

1 

3 

© 

to 

d 

03 

P$ 

CQ 

a 

5 

© 

to 

i 

« 

s 

a 

’e 

a 

© 

bJ3 

d 

C3 

« 

Altapass: 

No.  1,  base  station,  elevation  2,230... 

95 

16 

79 

95 

3 

92 

96 

16 

80 

90 

9 

81 

No.  2,  SE . .' . ' . 

250 

96 

14 

82 

95 

5 

90 

93 

15 

78 

91 

8 

83 

No.  3,  SE . 

500 

92 

14 

78 

93 

4 

89 

90 

15 

75 

86 

8 

78 

No.  4,  SE . 

750 

92 

12 

80 

92 

2 

90 

90 

13 

77 

86 

4 

82 

No.  5,  summit . 

1,000 

92 

10 

82 

91 

0 

91 

92 

12 

80 

86 

4 

82 

Asheville: 

No.  1,  base  station,  elevation  2,445... 

94 

10 

84 

92 

3 

89 

90 

15 

75 

89 

4 

85 

No.  2,  N . 

155 

94 

11 

83 

92 

2 

90 

90 

15 

75 

87 

3 

84 

No.  2a,  S . 

155 

93 

11 

82 

91 

3 

88 

89 

15 

74 

88 

5 

83 

No.  3,  N . 

380 

91 

11 

80 

90 

2 

88 

85 

13 

72 

83 

5 

78 

No.  3a,  S . 

380 

96 

11 

85 

95 

3 

92 

94 

14 

80 

90 

5 

85 

Blantyre: 

No.  1,  base  station,  elevation  2,090... 

98 

9 

89 

94 

—6 

100 

91 

12 

79 

93 

3 

96 

No.  2,  NW . 

300 

98 

10 

88 

93 

-3 

96 

90 

13 

77 

92 

0 

92 

No.  3,  NW . 

450 

97 

10 

87 

93 

0 

93 

90 

14 

76 

93 

5 

88 

No.  4,  NW . 

600 

97 

11 

86 

95 

1 

94 

90 

14 

76 

90 

6 

84 

Blowing  Rock: 

No.  1,  base  station,  elevation  3,130... 

90 

7 

83 

89 

1 

88 

84 

12 

72 

84 

2 

No.  2,  S . 

450 

88 

6 

82 

88 

0 

88 

86 

10 

76 

85 

3 

82 

No.  3,  SE . 

450 

88 

2 

86 

88 

1 

87 

87 

7 

80 

83 

-3 

86 

No.  4,  SE . 

625 

89 

6 

83 

88 

0 

88 

87 

9 

78 

82 

-1 

83 

No.  5,  SE . 

800 

88 

5 

83 

87 

-5 

92 

85 

7 

78 

81 

-2 

83 

Bryson: 

No.  1,  base  station,  elevation  1,800... 

97 

19 

78 

96 

2 

94 

92 

11 

81 

92 

No.  2,  N . 

385 

97 

21 

76 

96 

2 

94 

92 

12 

80 

92 

5 

87 

No.  2a,  S . 

385 

97 

20 

77 

96 

2 

94 

93 

13 

80 

92 

4 

88 

No.  3,  summit . 

570 

95 

22 

73 

96 

1 

95 

92 

14 

78 

95 

5 

90 

Cane  River: 

No.  1,  base  station,  elevation  2,650... 

93 

10 

83 

92 

3 

89 

88 

11 

No.  2,  N . 

190 

93 

13 

80 

90 

2 

88 

86 

11 

75 

86 

2 

84 

No.  3,  NE . 

400 

93 

12 

81 

90 

0 

90 

85 

10 

75 

86 

3 

83 

No.  4,  summit . 

1, 100 

94 

8 

86 

93 

1 

92 

90 

8 

72 

87 

0 

87 

Ellijay: 

No.  1,  base  station,  elevation  2,240... 

95 

10 

85 

94 

2 

92 

92 

No.  2,  N . 

310 

95 

10 

85 

93 

i 

92 

91 

14 

77 

89 

5 

oo 

84 

No.  3,  N . 

620 

92 

12 

80 

90 

i 

89 

89 

13 

76 

87 

5 

82 

No.  4,  N . 

1,240 

90 

11 

79 

90 

3 

87 

89 

12 

77 

84 

7 

77 

No.  5,  summit . 

Globe: 

1,760 

88 

0 

88 

90 

9 

82 

86 

4 

82 

No.  1,  base  station,  elevation  1,625... 

97 

13 

84 

96 

7 

89 

No.  2,  E . 

300 

97 

14 

83 

94 

7 

87 

94 

17 

77 

95 

8 

87 

No.  3,  summit . 

1,000 

98 

12 

86 

97 

6 

91 

94 

16 

78 

96 

7 

89 

1913-1916. 


96  3 

96  5 

92  4 

92  2 

92  0 


94 

94 

93 

91 

96 

98 

98 

97 
97 

90 

88 

88 

89 
88 

97 

97 

97 

96 

93 

93 

93 

94 

95 
95 

92 

90 
90 

97 

97 

98 


3 

2 

3 

2 

3 

-6 

-3 

0 

1 

1 

0 

-3 

-1 

-5 

2 

2 

2 

1 

-5 

2 

0 

0 

2 

1 

1 

3 

0 

7 

7 

6 


1  No.  5  not  established  in  1913. 


Range. 

Dates 
of  absolute 
maxima. 

Dates 
of  absolute 
minims. 

93 

July  31,  1915... 

Dec.  16, 1914. 

91 

July  19,1913... 

Dec.  15, 1914. 

88 

Mar.  2,  1914. 

90 

. do . 

Dec.  15, 1914. 

92 

July  19,  1913; 

Dec.  15,  16 

July  31, 1915. 

1914. 

91 

July  19,1913... 

Dec.  15,1914. 

92 

Do. 

90 

Do. 

89 

Do. 

93 

. do . 

Do. 

104 

Do. 

101 

. do . 

Do. 

97 

Do. 

96 

Do. 

89 

Do. 

88 

. do . 

Do. 

91 

Jan.  18,  1916. 

90 

Do. 

93 

. do . 

Dec.  15, 1914. 

95 

July  18,1913... 

Do. 

95 

. do . 

Do. 

95 

. do . 

Do. 

95 

June  11,1914. . 

Do. 

98 

July  18,1913.. 

Dec.  19, 1916. 

91 

. do . 

Dec.  15, 1914. 

93 

July  19,1913... 

Do. 

94 

Dec.  19,1914. 

93 

Julv  18,1913... 

Dec.  15, 1914. 

94 

. do . 

Do. 

91 

July  IS,  19, 

Do. 

1913. 

87 

Mar.  2,  1914. 

90 

July  31, 1915  i . 

Do. 

90 

July  18,  19, 

Dec.  15, 1914. 

1913. 

90 

July  19,1913... 

Do. 

92 

Do. 

THERMAL  BELTS  AND  fruit  GROWING  IN  NORTH  CAROLINA.  49 

T"  *  **>  -  -**  «*  ****** 

_ _ fTh6  diff6renC6S  b6tWee°  thg  aV6rageS  8t  the  base  Stati0n  and  *»>*■  of  the  respective  slope  stations  may  be  seen  by  shnpie  inspection., 


Principal  and  slope  stations;  elevation  of 
base  stations  above  mean  spa  level 
(feet). 


Gorge; 

No.  1,  base  station,  elevation  1,400 

No.  2,  NE . 

No.  3,  S .  . 

?N  (old). 


No-  {ne.  (new). 


No.  5,  summit.. . 

Hendersonville: 

No.  1,  base  station,  elevation  2,200.. 

No.  2,  E . 

no.  3,  e . 

No.  4,  summit. . ’ 

Highlands: 

No.  1,  base  station,  elevation  3,350.. 

No.  2,  SE . . 

No.  3,  SE .  . 

No.  4,  SE . 

No.  5,  SE . 

Mount  Airy: 

No.  1,  base  station,  elevation  1,340.. 

No.  2,  W . . . 

No.  3,  E . 


No.  4,  summit . 

Transon: 

No.  1,  base  station,  elevation  2,970. 

No.  2,  W . 

No.  3,  W . 

No.  4,  summit . 

Try on: 

No.  1,  base  station,  elevation  950. . . 

No.  2,  SE . 

No.  3,  SE . 

No.  4,  SE . 

Wilkesboro: 

No.  1,  base  station,  elevation  1,240.. 
No.  2,  N . 


of 

slope 

station: 

above 

base 

(feet), 


290 

615 

840 

1,040 


450 

600 

750 


No.  3,  N. 
No.  4,  W. 


200 

325 

525 

725 


160 

160 


360 


150 

300 

450 


380 
570 
1, 100 


150 


350 

430 


4913 

1914 

1  Maximum. 

I  Minimum. 

Range. 

Maximum. 

Minimum. 

Range. 

101 

13 

88 

98 

5 

93 

99 

11 

88 

97 

4 

93 

96 

10 

86 

93 

6 

87 

98 

11 

87 

94 

7 

87 

100 

12 

88 

95 

9 

86 

97 

11 

86 

93 

1 

92 

95 

14 

81 

90 

4 

86 

94 

13 

81 

91 

1 

90 

94 

14 

80 

90 

1 

89 

90 

12 

78 

89 

2 

87 

90 

12 

78 

90 

2 

88 

88 

6 

82 

85 

-7 

92 

87 

9 

78 

88 

-2 

90 

89 

9 

80 

88 

-2 

90 

95 

9 

86 

99 

9 

90 

96 

9 

87 

99 

8 

91 

95 

10 

85 

98 

8 

90 

95 

12 

83 

98 

7 

91 

91 

4 

87 

92 

-4 

96 

91 

5 

86 

90 

1 

■  89 

91 

5 

86 

91 

1 

90 

88 

4 

84 

90 

0 

90 

103 

15 

88 

100 

13 

87 

103 

19 

84 

101 

12 

89 

102 

18 

84 

99 

10 

89 

101 

16 

0' 

98 

7 

A 

101 

14 

87 

99 

6 

93 

102 

14 

88 

100 

8 

92 

100 

14 

86 

99 

10 

89 

100 

13 

87 

98 

8 

90 

1915 


98 

97 
93 

95 

95 

92 

90 

90 

89 

87 

87 

82 

86 

87 

100 

99 
99 

99 

90 

88 
89 
86 

99 

99 

98 

96 

99 
98 


95 

96 


16 

15 

14 

16 

15 

12 

13 

13 

14 

11 

11 

3 

5 

5 

16 
16 
17 

16 


14 
11 
11 

16 

21 

19 

17 

15 
15 


17 

16 


« 


82 

82 

79 

79 

80 

80 

77 

77 

75 

76 
76 
79 
81 
82 

84 

83 

82 

83 

81 

74 

78 

75 

83 

78 

79 
79 

84 
83 


78 

80 


1916 

1913-1916. 

Dates 
of  absolute 
maxima. 

Maximum. 

Minimum 

Range. 

Maximum. 

Minimum. 

Range. 

97 

7 

90 

101 

5 

96 

July  19, 1913... 

92 

9 

83 

99 

4 

95 

93 

5 

88 

96 

5 

91 

. do . 

91 

9 

82 

98 

7 

91 

. do . 

91 

12 

79 

100 

9 

91 

90 

4 

86 

97 

1 

96 

88 

6 

82 

95 

4 

91 

89 

2 

87 

94 

1 

93 

. do . 

87 

4 

83 

94 

1 

93 

. do . 

87 

8 

79 

90 

2 

88 

87 

5 

82 

90 

2 

88 

. do . 

85 

0 

85 

88 

— 

7 

95 

July  18, 1913... 

85 

3 

82 

88 

— 

2 

90 

June  12, 1914. 

85 

3 

82 

89 

— 

2 

91 

July  19, 1913. 

91 

7 

84 

100 

7 

93 

July  31,  1915... 

91 

10 

81 

99 

i 

91 

. do.. . 

92 

8 

84 

99 

8 

91 

. do . 

92 

11 

81 

99 

7 

92 

. do . 

86 

3 

83 

92 

- 

4 

96 

June  26,  1914.. 

83 

2 

81 

90 

1 

89 

. do . 

84 

3 

81 

91 

1 

90 

83 

3 

80 

90 

0 

90 

. do . 

97 

7 

90 

103 

7 

96 

July  19, 1913... 

95 

12 

83 

103 

12 

91 

. do . 

93 

10 

83 

102 

10 

92 

. do . 

91 

8 

83 

101 

7 

94 

- 

93 

5 

88 

101 

5 

96 

. do . 

93 

8 

85 

102 

8 

94 

. do . 

91 

12 

79 

100 

10 

90 

. do . 

91 

n 

80 

100 

8 

92 

. do . 

Dates 
of  absolute 
minima. 


Dec.  15,  1914. 
Do. 

Dec.  19,  1916. 
Dec.  15, 1914. 
Do. 

Dec.  16, 1914. 
Dec.  15, 1914. 
Do. 

Do. 

Mar.  2, 1914. 
Do. 

Dec.  15,  1914. 
Mar.  2, 1914. 
Do. 

Jan.  18, 1916. 
Dec.  27,  1914. 
Dec.  15,  1914; 

Jan.  18,  1916 
Dec.  27,  1914. 

Dec.  15  and  27, 
1914. 

Dec.  16, 1914. 
Dec.  15,  1914. 
Do. 

Dec.  20,  1916. 
Dec.  15,  1914. 
Do. 

Do. 

Dec.  20, 1916. 
Dec.  16,  1914; 
Jan.  18  and 
Dec.  20, 1916. 
Dec.  15, 1914. 
Do. 


RANGE  IN  TEMPERATURE. 

The  range  in  temperature  is  perhaps  not  of  much  im¬ 
portance  in  the  growing  of  fruit.  The  principal  factor  is 
the  minimum,  and  yet  the  maximum  is  also  a  factor, 
although  much  less  important.  The  range  simply  shows 
the  variation  between  the  two,  whether  for  the  year,  the 
month,  or  the  day. 

Of  course,  the  range  averages  the  least  where  the  mini¬ 
mum  is  highest  and  the  maximum  lowest,  and  the  range 
averages  the  greatest  where  the  minimum  is  lowest  and 
the  maximum  highest,  or  relatively  so.  We  know  from 
the  discussion  of  previous  tables  that,  with  only  a  few 
exceptions,  the  maximum  is  highest  and  the  minimum 
lowest  at  the  base  stations,  and  the  greatest  ranges  are 
usually  found  there.  However,  as  the  maximum  is  the 
least  sometimes  on  the  summit  and  at  other  times  at  a 
station  on  the  slope  lower  down  and  on  knobs  of  slight 
elevation,  and  the  minimum  highest  in  the  center  of  the 
thermal  belt,  located  either  on  the  slope  or  at  the  sum¬ 
mit,  there  is  necessarily  a  great  variation  in  the  position 
of  the  least  range. 

Absolute  range.— The  absolute  ranges  for  the  four-year 
period  for  all  the  stations  are  included  in  Table  3,  along 
with  the  absolute  maxima  and  minima. 

The  greatest  absolute  range  is  104°,  recorded  at  the 
base  station,  Blantyre  No.  1,  elevation  2,090  feet,  this 
range  being  the  difference  between  a  maximum  of  98° 
and  a  minimum  of  —  6°,  Reference  has  already  been 


made  to  the  fact  that  the  minima  at  the  Blantyre  base 
station  are  abnormally  low,  considering  the  moderate 
elevation  of  the  station  above  sea-level,  and  it  is  on  this 
account  that  the  range  is  so  large,  the  absolute  maximum 
of  98°  not  being  unusual.  The  least  absolute  range  is 
87°  at  Ellijay  No.  4,  3,480  feet  above  sea  level,  doubtless 
because  the  minimum  at  that  point  on  the  slope  is  rela¬ 
tively  high  during  nights  of  inversion,  as  it  is  well  within 
the  thermal  belt,  and  because  the  maximum  there  does 
not  rise  to  a  high  point  on  account  of  the  elevation  and 
the  northerly  inclination  of  the  slope. 

In  cities  near  sea  level  in  the  northern  States  of  this 
country  having  summer  minimum  temperatures  similar 
to  those  at  Highlands  and  Blowing  Rock  in  the  North 
Carolina  Mountain  Region,  winter  minima  of  25°  to  30° 
below  zero  and  even  lower  occur.  At  the  Weather 
Bureau  station  at  Albany,  N.  Y.,  for  instance,  which  has 
the  same  annual  mean  temperature  as  Blowing  Rock  No. 
3,  the  extremes  are  much  greater,  the  winters  being 
colder  and  the  summers  warmer. 

Although  the  mean  temperature  at  both  stations 
for  the  four-year  period  is  approximately  49°,  the  abso¬ 
lute  range  during  this  time  at  Albany  is  117°,  while  at 
Blowing  Rock  No.  3  it  is  only  91°.  Taken  as  a  whole, 
the  figures  in  Table  3  show  that  the  winters  are  much 
warmer  and  the  summers  much  cooler  in  this  mountain 
region  than  the  winters  and  summers  of  northern  cities 
near  sea  level  having  the  same  annual  mean  tempera¬ 
ture. 


50 


SUPPLEMENT  NO.  19. 


Figure  50  shows  graphically  the  absolute  and  annual 
ranges  for  the  six  long  slopes,  Altapass,  Cane  River, 
Ellijay,  Globe,  Gorge,  and  Tryon,  in  addition  to  the 
absolute  extremes  of  temperature  and  the  average  annual 
temperature  during  the  four-year  research.  Data  for 
Blowing  Rock  and  Highlands,  at  which  exceedingly  low 
temperatures  occur,  are  not  included,  as  the  stations  at 


~/o  O  /O  ZO  •SO  -0O  SO  <50  70  SO  <90  soo  /so 


Fio.  50.— Absolute  and  average  annual  maximum  and  minimum  temperatures  and 
range,  six  long  slopes.  Solid  lines  show  extremes;  shaded,  averages. 

both  these  places  are  in  two  groups  located  on  different 
slopes  nor  is  any  other  short  slope  included. 

There  is  a  certain  uniformity  apparent  in  the  varia¬ 
tion  of  the  range  on  these  long  slopes.  The  largest 
absolute  ranges  are  found  at  the  base  stations  at  .Aita- 
pass,  Cane  River,  Gorge,  and  Tryon,  while  the  least  in 
every  case  is  at  some  point  on  the  slope  in  the  thermal 
belt.  The  largest  range  at  Globe  is  on  the  summit,  because 
of  the  high  maxima  registered  there,  while  the  largest 


at  Ellijay  is  at  station  No.  2,  which  has  the  lowest  minima 
on  this  slope  above  the  base. 

Average  annual  range  in  temperature. — The  variation 
in  average  annual  range  in  temperature  on  the  six  long 
slopes,  as  illustrated  in  Figure  51,  conforms  roughly  to 
the  variation  in  absolute  range. 

The  greatest  and  least  absolute  ranges  and  the  greatest 
and  least  average  annual  ranges  do  not,  of  course,  neces¬ 
sarily  coincide,  because  the  former  are  often  due  to  unu¬ 
sual  and  even  abnormal  conditions,  while  the  latter  are 
the  result  of  all  conditions,  both  normal  and  abnormal. 

Daily  range — Seasonal  variation. — For  lack  of  space  the 
table  compiled  to  show  the  average  daily  range  of  tem¬ 
perature  on  all  slopes  is  omitted  in  this  publication,  but, 
nevertheless,  the  material  may  be  discussed  briefly. 

The  greatest  daily  ranges  usually  occur  at  the  base 
stations  in  months  most  favorable  for  inversions — May 
and  November — when  the  maxima  are  relatively  high 
and  the  minima  low  under  the  influence  of  clear  weather, 
especially  on  the  valley  floors.  The  least  average  daily 
ranges  are  found  in  the  thermal  belt,  either  on  the  slopes 
or  at  the  summits  and  usually  in  January  and  December, 
months  with  considerable  cloudiness  and  storm  activity, 
unfavorable  for  frequent  inversions,  although  with  large 
ranges  on  individual  clear  days.  While  the  small  range  in 
the  thermal  belts  is,  as  a  rule,  due  to  the  high  minima 
found  there  on  nights  of  inversion,  sometimes  because  of 
special  local  conditions,  such  as  those  at  the  No.  3  stations 
at  Asheville  and  Cane  River,  a  low  maximum  is  equally 
important.  At  Altapass  and  Tryon  the  middle  of  the 
thermal  belt  is  usually  located  between  Nos.  2  and  3,  and 
at  No.  3  in  both  places  are  found  the  least  average  daily 
ranges,  17.9°  and  18.0°,  respectively.  At  Ellijay  the 
smallest  average  daily  range,  17.0°,  occurs  atNo.4,  and  this 
is  not  only  because  of  the  relatively  high  minima  recorded 
there  during  inversion  conditions,  but  also  because  of  com¬ 
paratively  low  maxima  during  a  portion  of  the  year,  as 
explained  under  the  discussion  of  "Average  maximum 
temper atme.”  The  center  of  the  thermal  belt  at  Cane 
River  lies  between  Nos.  3  and  4,  and  at  the  former  station 
is  found  the  smallest  average  daily  range  on  that  slope, 
19.2°,  but  this  is  the  result  of  a  combination  of  relatively 
high  minima  due  to  frequent  inversions  and  relatively  low 
maxima  due  to  local  exposure,  as  already  explained.  It 
can  be  seen,  then,  that  the  least  average  daily  range  is 
generally  coincident  with  the  highest  average  minima, 
which,  in  turn,  are  found  at  points  locating  the  middle  of 
the  thermal  belt  during  inversion  conditions,  although 
unusually  low  maxima  are  sometimes  factors. 

While  the  base  station  at  Blantyre  registered  the 
greatest  absolute  range  in  the  four-year  period,  the  group 
at  Bryson,  as  a  whole,  has  the  greatest  average  daily  range, 
probably  on  account  of  both  the  unusually  low  minima  in 
this  broad  frost  pocket  and  the  high  maxima  due  to  the 
moderate  elevation  of  the  group.  The  greatest  annual 
average  daily  range  at  any  one  station  at  Bryson,  27.1°, 
occurs  at  the  base,  this  being  greater  than  at  any  other 
station  in  the  research.  Furthermore,  the  annual  average 
daily  range  at  Bryson,  station  for  station,  is  greater  than 
on  any  other  slope,  and  this  also  can  be  said  for  the 
monthly  average  daily  range,  as  a  rule.  The  four-year 
annual  daily  ranges  at  the  base  stations  at  Blantyre, 
Ellijay,  and  Gorge  are  relatively  large,  being,  respectively, 
26.2°,  26.6°,  and  25.6°.  It  will  be  noted  that  in  each  of 
these  instances,  including  Bryson,  the  base  stations  are 
located  on  true  valley  floors,  where  the  exposure  insures 
high  maxima  on  days  with  clear  weather  and  low  minima 
during  nights  of  inversion  and  where  the  elevation  above 
sea  level  is  not  necessarily  low.  Moreover,  the  vegeta- 


51 


THERMAL  BELTS  AND  FRUIT 

tion  in  anv  group  is  usually  densest  at  the  base,  trapping 
the  heated  air  auring  days  of  sunshine  and  insuring  great 
loss  of  heat  through  radiation  at  night. 

The  least  average  daily  range  in  a  group  as  a  whole 
occurs  at  Blowing  Rock,  and  the  ranges  at  Highlands, 
with  the  exception  of  No.  3,  are  nearly  as  small.  Of  the 
five  stations  at  Blowing  Rock  the  lowest  average  occurs 
at  No.  2,  16.8°.  At  Highlands  the  least  average  daily  range 
occurs  at  Nos.  1  and  2,  the  figures  being  17.6°  for  each 
station.  In  general,  the  smallest  ranges  occur  practically 
always  in  the  most  elevated  groups,  because,  in  addi¬ 
tion  to  Blowing  Rock  and  Highlands,  the  higher  sta¬ 
tions  at  Transon,  Ellijay,  Cane  River,  and  Altapass  have 
comparatively  small  daily  ranges. 

However,  the  smallest  average  daily  range,  16.4°,  of 
all  the  stations  in  the  region  is  noted  at  Asheville  No.  3, 
shut  in  by  timber  on  a  northerly  slope,  2,825  feet  above 
sea  level,  but  this  range,  which  is  1.4°  lower  than  the 


GROWING  IN  NORTH  CAROLINA. 

variation  in  the  range  between  the  base  and  the  summit 
and  can  be  used  to  better  advantage  in  comparisons. 
This  graph  will  serve  to  supplement  the  previous  discus¬ 
sion.  In  every  case  the  largest  average  range,  bothseasonal 
and  annual,  is  seen  to  be  at  the  base  stations,  while  the 
osition  of  the  least  range  on  the  slope  varies,  always 
eing,  however,  approximately  near  the  center  of  the 
thermal  belt. 

The  largest  average  daily  range  for  these  six  slopes  in 
any  month,  as  shown  by  the  graph,  is  30.3°,  in  April  at 
Gorge  station  No.  1,  wliile  the  smallest  average  in  any 
month  is  13.3°  in  January  at  Ellijay  Station  No.  4, 
located  1,240  feet  above  the  valley  floor.  Moreover,  the 
smallest  average  daily  range  for  the  four  years,  17°,  is  at 
the  same  station  at  Ellijay,  while  the  largest  average  for 
the  entire  period,  26.6°,  is  also  at  Ellijay,  but  at  the  base 
station,  the  latter,  in  fact,  registering  a  considerable 
range  in  all  months  of  the  year.  This  comparison,  of 


Fig.  51.— Average  daily  range  in  temperature,  six  long  slopes.  The  numbers  at  the  bottom  represent  the  several  slope  stations. 


range  for  the  same  length  of  time  at  the  highest  elevation 
in  the  research,  Highlands  No.  5,  is  due  largely  to  the 
remarkably  low  maxima,  as  already  stated,  but  its  high 
minima  are  also  a  factor,  as  the  station  is  located  well 
within  the  thermal  belt  during  nights  of  inversion. 

In  general,  then,  the  statement  of  Hann  4  in  his  Hand¬ 
book  of  Climatology  that  “the  amount  of  range  in  tem- 
erature  generally  decreases  with  increasing  elevation” 
olds  good  for  this  region,  because  these  observations 
would  definitely  show  this  to  be  the  case  were  the  environ¬ 
ments  of  the  stations  comparable,  aside  from  elevation. 

Figure  51  shows  the  average  daily  variation  in  range, 
seasonal  and  annual,  on  the  six  long  slopes,  Altapass, 
Cane  River,  Ellijay,  Globe,  Gorge,  and  Try  on.  For 
convenience  the  months  of  January,  April,  July,  and 
October  are  chosen  as  representative  of  the  various 
seasons.  Long  slopes  show  marked  uniformity  in  the 

<  Hann,  Dr,  Julius,  "Handbook  of  Climatology,”  pp.  273-274.  English  translation 

by  Ward. 


course,  has  reference  to  the  six  long  slopes  only,  because 
it  has  already  been  shown  that,  for  the  entire  region,  the 
greatest  average  daily  range  for  the  4-year  period  is 
27.1°,  at  Bryson  station  No.  1,  and  the  smallest,  16.4°, 
at  Asheville  No.  3. 

The  average  daily  range  in  temperature,  whether  for 
the  months  or  for  the  year,  does  not  indicate  much  as  to 
the  largest  ranges  that  may  be  observed  in  a  single  day, 
as  individually  daily  ranges  are  much  greater.  In  the 
four-year  period  of  the  research  for  the  entire  region, 
embracing  all  stations,  the  largest  range  in  one  day  was 
52°,  observed  at  Blantyre  station  No.  1  on  November  13, 
1913.  Other  relatively  large  ranges  were  51°  at  Bryson 
No.  1  on  April  19,  1916;  48°  at  Gorge  No.  1  May  1,  1916; 
and  47°  at  Elijay  No.  1  May  21,  1914  all  four  during  clear 
weather  favorable  for  large  inversions.  On  the  other 
hand,  the  smallest  daily  ranges  observed  were  1°  at 
Ellijay  No.  4  January  3,  1914,  and  2°  at  Asheville  No.  3 
January  2,  1914,  both  during  cloudy  weather. 


52 


SUPPLEMENT  NO.  19. 


The  range  in  temperature,  of  course,  depends  largely 
upon  the  weather  conditions,  there  being  much  greater 
range  during  periods  of  sunshine  than  in  cloudy  weather. 
In  clear  weather  the  maximum  temperature  rises  to  a 
high  point  and  the  minimum  falls  correspondingly  low, 
thus  permitting  a  considerable  range;  but  during  cloudy 
weather,  when  the  sunshine  is  shut  off,  the  maximum 
during  the  daytime  is  rather  low,  and  at  night  the  mini¬ 
mum  is  high,  as  the  loss  of  heat  by  radiation  with  the 
sky  obscured  is  comparatively  small. 

So  in  Figure  51  we  have  seen  that  the  largest  daily 
ranges  occur  in  the  spring  and  autumn  at  the  time  of 
largest  inversions,  when  the  weather  conditions  are  most 
settled.  The  greatest  average  daily  ranges  are  shown  to 
be  in  the  months  of  April  and  October,  while  the  least  are 
recorded  in  January,  usually  stormy  and  cloudy,  and  in 
July,  with  a  high  percentage  of  cloudiness  and  with  small 
inversions,  April  having  the  largest  ranges  and  January 
the  smallest.  Doubtless,  the  range  is  low  in  January 
because  of  the  comparatively  high  minima  and  in  July 
because  of  the  comparatively  low  maxima.  Moreover, 
in  April  and  October,  the  months  of  greatest  range,  the 
maxima  are  comparatively  high  and  the  minima  low. 

MEAN  TEMPERATURE. 

Monthly  and  annual  mean  temperatures. — -The  figures 
in  Table  4  have  been  computed  from  the  true  means  of 
the  maximum  and  minimum  temperatures.  In  the 
mountain  region  there  is  no  uniformity  in  the  variation 
of  mean  temperature  with  elevation,  and  this  is  because 
of  the  great  irregularities  in  both  the  maximum  and 
minimum  temperatures  on  the  various  slopes,  particu¬ 
larly  the  latter.  On  this  account  it  hardly  seems  advis¬ 
able  to  discuss  the  mean  temperatures  at  any  great 
length. 

It  is  apparent  at  a  glance  that  the  mean  temperature 
does  not  decrease  with  elevation  at  any  uniform  rate  and 
that  in  some  instances  there  is  even  an  increase  with 
elevation,  largely  because  of  the  frequent  periods  of  in¬ 
version,  at  which  times  the  base  station  is  the  coldest. 

It  seems  necessary  to  touch  only  briefly  upon  the 
variation  in  the  readings  on  the  individual  slopes.  A 
cursory  inspection  of  the  differences  between  the  means 
of  base  stations  and  those  of  the  respective  slopes  in¬ 
dicates  that  sometimes  the  lowest  mean  is  at  the  base 


station,  at  other  times  at  the  summit,  and  at  still  other 
times  at  some  point  midway  between.  Where  there  are 
base  stations  located  in  distinct  frost  pockets,  as  at  stations 
No.  3  at  both  Blowing  Rock  and  Highlands  and  stations 
No.  1  at  both  Blantyre  and  Bryson,  the  lowest  means 
will  be  found  there,  and,  as  previously  shown,  these 
stations  have  also  the  lowest  four-year  average  minima. 
On  such  slopes  as  Mount  Airy  and  Wilkesboro  the  mean 
averages  the  lowest  at  the  base,  and  on  the  long  slopes,  as 
at  Altapass,  Ellijay,  and  Tryon,  the  mean  annual  tem¬ 
perature  is  generally  lowest  at  the  summit.  But  where 
there  are  coves  or  frost  pockets  on  long  slopes,  as  at 
station  No.  3  at  Cane  River  and  Nos.  2  and  3  at  Gorge, 
the  lowest  means  will  be  at  those  points,  instead  of  at 
the  summits.  Generally,  the  variation  in  mean  tem¬ 
perature  on  a  slope  depends  more  upon  the  variation  in 
minimum  temperature  than  upon  the  maximum,  but 
station  No.  3  at  Asheville,  a  slope  station,  owes  its  low 
mean  solely  to  the  low  maximum,  where  the  shelter  is 
on  a  northerly  slope  with  timber  above,  which,  as  stated 
previously,  shuts  off  the  sunshine  practically  all  the  time. 
Moreover,  the  low  mean  at  Cane  River  No.  3,  referred  to 
above,  is  largely  due  to  the  low  maxima  at  times  when 
the  sunshine  is  shut  off  early. 

The  highest  mean  temperatures  are  found  invariably 
at  some  point  above  the  base  and  in  no  case  is  the  highest 
annual  mean,  and  seldom  even  the  mean  in  any  month, 
found  on  the  valley  floor.  Whether  the  highest  is  found  on 
the  slope  or  at  the  summit,  the  place  is  usually  coincident 
with  the  center  of  the  thermal  belt  during  nights  of  in¬ 
version,  this  being  the  level  of  the  least  average  range, 
as  well.  Thus  on  most  of  the  slopes  where  the  thermal 
belts  are  centered  at  the  summit,  as  Blantyre,  Bryson, 
Gorge,  and  Hendersonville,  the  highest  mean  tempera¬ 
tures  are  found  at  those  levels,  although  in  some  other 
cases,  as  Cane  River,  Mount  Airy,  and  Wilkesboro,  the 
highest  mean  temperatures  are  lower  down  on  the  slope, 
in  the  latter  instances  the  influence  of  the  maximum 
temperature  counteracting  that  of  the  minimum.  The 
minimum,  however,  as  stated  before,  stands  out  most 
prominently  as  the  factor  affecting  the  position  of  the 
mean  temperature,  as  shown  not  only  by  the  number 
of  places  having  the  highest  mean  at  the  summit,  but 
also  by  certain  other  places  where  the  highest  mean  is 
lower  down  on  the  slope,  as  at  Altapass  and  Tryon  near 
Stations  No.  2  in  the  center  of  the  thermal  belt. 


Table  4. — Monthly  and  annual  mean  temperatures,  1913-1916. 


Principal  and  slnpe  stations, 
elevation  base  station  above 
mean  sea  level  (feet). 


Altapass: 

No.  1,  base  station,  eleva¬ 
tion  2,230 . . 

No.  2,  SE . . 

No.  3,  SE . 

No.  4,  SE . 

No.  5,  summit . 

Asheville: 

No.  1,  base  station,  eleva¬ 
tion  2,445 . 

No.  2,  N . 

No.  2a,  S . 

No.  3,  N . 

No.  3a,  S . 

Blantyre: 

No.  1,  base  station,  eleva¬ 
tion  2,090 . 

No.  2,  NW . 

No.  3,  NW . . 

No.  4,  NW . 


Height 
of  slope 
stations 
above 
base 
(feet). 

Janu¬ 

ary. 

Febru¬ 

ary. 

March. 

April. 

May. 

June. 

i  39.6 

i  38.4 

1  41.4 

i  55.1 

64.2 

69.0 

250 

i  39.4 

■  38.3 

3  40.9 

*  55.3 

64.6 

69.4 

500 

t;38.  5 

137.4 

3  39.8 

i  53.9 

63.6 

68.2 

750 

1  36.9 

l  35.7 

3  40.  4 

i  52.4 

62.0 

66.6 

1,000 

36.4 

35.2 

38.0 

52.0 

61.0 

65.8 

155 

41.7 

38.9 

42.7 

53.7 

63.2 

68.2 

41.4 

38.4 

42.4 

54.2 

64.2 

68.6 

155 

42.4 

39.3 

43.1 

55.0 

64.2 

68.9 

380 

40.7 

37.8 

41.8 

54.0 

64.2 

68. 1 

380 

42.4 

39.8 

43.6 

55.9 

65.6 

69.8 

300 

41.4 

39.1 

43.4 

53.6 

63.1 

69.2 

41. 1 

38.7 

43.6 

54.9 

63.9 

68.8 

450 

41.6 

39.4 

43.7 

55.6 

65.0 

69. 1 

600 

42.4 

40.7 

44.6 

57.1 

66.1 

70.1 

*  3-year  average. 

July. 

August. 

Septem¬ 

ber. 

October. 

Novem¬ 

ber. 

Decem¬ 

ber. 

4-year 

animal. 

72.3 

71.3 

64.6 

57.4 

47.9 

38.5 

‘  54.9 

72.2 

71.2 

65.2 

58.2 

48.2 

38.4 

>  55. 1 

71.0 

70.2 

64. 1 

56.  8 

47. 1 

37.2 

*  53.9 

69.4 

68.9 

62.4 

55.7 

45.9 

35.6 

>  52.7 

69. 1 

68.2 

62.0 

54.6 

45.2 

35.3 

i  51.8 

71.2 

70.7 

64.6 

56.8 

47.2 

38.5 

54.8 

71.1 

70.3 

64.9 

56.3 

47. 1 

38.0 

54.8 

71.5 

71.0 

65.6 

57.6 

48.3 

39.4 

55.5 

70.6 

69.5 

63.2 

55.6 

46.8 

37.5 

54.2 

72.3 

71.5 

65.7 

58.2 

50.0 

39.6 

56.2 

72.2 

71.5 

64.6 

56.1 

45.2 

37.3 

54.7 

71.4 

70.6 

63.9 

55.6 

45.8 

37.4 

54.9 

71.8 

70.9 

64.2 

57.0 

47.9 

38.2 

55.4 

72.9 

72.0 

66.0 

58.4 

49.4 

39.2 

56.6 

J  2-year  average. 


THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 

Table  4.— Monthly  and  annual  mean  temperatures,  1913-1916 — Continued. 


Principal  and  slope  stations, 
elevation  base  station  above 

Height 
of  slope 

stations 

Janu- 

Febru- 

March. 

April. 

mean  sea  level  (feet). 

above 

base 

(feet). 

ary. 

ary. 

May. 

June. 

July. 

August. 

Septem¬ 

ber. 

October. 

Novem¬ 

ber. 

Decem¬ 

ber. 

4-year 

annual. 

Blowing  Rock: 

No.  1,  base  station,  eleva- 

tion  3,130 . 

38.5 

50.6 

No.  2,  S . 

35.  0 

34.6 

32.6 

33.7 

32.8 

60.3 

65.9 

68.  8 

68.0 

67.6 

65.2 

66.9 

66.4 

44.2 

45.0 

40.9 

34.8 

35.1 
32.7 

34.2 

33.2 

51.6 

No.  3,  SE  base  sta _ 

450 

38. 1 

50.8 

60.9 

66.0 

68.6 

61.6 

.58.3 

No.  4,  SE . 

36.4 

47.9 

57.4 

63.4 

66.0 

do.  47 

51. 6 

No.  5,  SE . 

37. 1 

49.3 

59.5 

64.8 

68.0 

49.0 

Bryson: 

No.  1,  base  station,  eleva- 

36. 6 

48.7 

58.9 

64.4 

67.3 

6oio 

52.4 

42.8 

50. 6 
50.0 

tion  1 ,800 . 

54.6 

No.  2,  N . 

1  39.9 

1  41.  7 

1  42.2 

1  42.9 

1  43.7 

64.0 

69.7 

72.8 

72.3 

66.3 
66. 1 
66.  2 

55.3 

55.4 

No.  2a,  S . 

55.3 

64.7 

69.4 

72.3 

71.8 

57.7 

57.8 

57.9 

No.  3,  summit _ 

570 

1  40.  7 

56.3 

65.2 

69.9 

72.6 

72.2 

Cane  River: 

58.7 

67.2 

70.9 

73.3 

72.3 

66.3 

1 4a  2 

‘  37.6 

56.6 

No.  1,  base  station,  eleva- 

tion  2,650 . 

51.0 

60.8 

No.  2,  N . 

190 

1  38. 3 

1  39.0 

1  37.7 

2  36.  2 

66.4 

69.8 

69.4 

62.5 

53.9 
54.  7 

43.3 

45.4 
43.9 
45.6 

No.  3,  NE . 

52.4 

62. 1 

67.0 

69.9 

69.2 

62.6 

No.  4,  summit . 

1, 100 

■  36.7 

52.3 

62.4 

66.9 

69.6 

68.5 

61.6 

53.3 

34.5 

35.0 

Ellijay: 

52. 0 

63.0 

67.0 

69.6 

68.4 

62.0 

54.2 

52.0 

No.  1,  base  station,  eleva- 

tion  2,240 . 

i  41.0 

,  Jt  , 

54.2 

63.2 

68.3 

71.4 

No.  2,  N . 

1  42.0 

1  41.3 

70.8 

64.8 

56.4 

46.3 
47. 1 

38.6 

38.8 

38.9 
37.8 

No.  3,  N* . 

620 

1,240 

1,760 

55.  4 

64.2 

68.7 

71.4 

70.4 

64.7 

56.4 

55.0 

54.7 

54.2 

53.3 

No.  4,  N.. . 

54.  8 
54.6 

1  53.7 

64. 1 

68.2 

70.7 

69.8 

64. 1 

56.4 

47.9 

No.  5,  summit . 

2  39.  5 

64.3 

1  63.5 

68.2 

70.6 

69.6 

64.0 

56.3 

47.5 

Globe: 

1  66.8 

1  68.8 

1  68.5 

63.4 

1  56.3 

1  46.6 

>  36.1 

No.  1,  base  station,  eleva- 

tion  1.625 . 

41.0 

40.7 

41.0 

64.8 

70.1 

73.2 

72.2 

No.  2,  E . 

300 

1,000 

4x).  0 

55. 0 
56.5 
56.7 

65.9 

58.4 

47.6 

38.7 

55.8 

No.  3,  summit _ 

66.  4 
66.8 

70.4 

70.6 

73.2 

72.1 

66.2 

58.7 

48.4 

3a  4 

56.2 

Gorge: 

40.  O 

73.3 

71.9 

65.6 

58.5 

49.0 

38.3 

56.2 

No.  1,  base  station,  eleva¬ 
tion  1.400 . 

40.5 

40.4 

40.8 

40.7 

40.8 

39.6 

65.2 

64.7 

64.7 

66.4 

67.0 

70.5 

69.7 
69.0 
70.3 

70.8 

73.8 

72.7 

66.0 

No.  2,NE . 

290 

615 

840 

1,040 

Od.  O 

54.9 

55. 5 

56.6 

58.2 

46.9 

37.7 

55.9 

No.  3,  S . 

72.9 

72.2 

65.2 

57.5 

47.0 

37.9 

55.5 

No.  4,  N.  (old),  NE.  (new).. 
No.  5,  summit . 

39.3 

39.6 

43.8 

43.7 

72.  2 
73.0 
73.5 

71. 1 
72.0 
72.0 

64.  7 
65.4 

57.2 

57.9 

48.0 

48.6 

38.2 

38.1 

55.4 

56.0 

Hendersonville: 

65. 6 

58.3 

48.6 

38.7 

56.3 

No.  1,  base  station,  eleva- 

tion  2,200.... 

1  39. 1 
139.5 
139.5 
139.5 

138.5 

137.8 
138.1 

137.9 

1  41.4 
140.9 
140.7 
140.5 

71.3 

70.9 

71.0 

71.2 

70.6 

69.9 

69.9 

70.1 

63.4 

55.6 

45.3 

No.  2,  E . 

450 

600 

750 

Od,  d 

O^.  O 

63.0 

63.7 

68.2 

68.3 

37.4 

53.9 

No.  3,  E . 

63.  4 

55. 6 

46.1 

37.5 

53.8 

No.  4,  summit . 

54.1 

63.6 

64.2 

56. 0 

46.3 

36.8 

54.1 

Highlands: 

56. 6 

47.8 

37.6 

54.3 

No.  1,  base  station,  eleva- 

tion  3,350 . 

1  39.5 

>36.2 

139.3 

133.0 

143.3 

1  40.4 
135.8 

53.7 

53.6 

47.9 

63.5 

63.6 
57.5 

55.8 

56.1 

50.2 

47.5 

38.6 

53.6 

No.  2,  SE . 

200 

325 

140.7 
*  37.5 

69.6 

69.2 

64.0 

No.  3,  SE  base  sta . 

Dd.  O 

57.1 

61.6 

47.  8 
41.3 

39. 6 
34  0 

54. 1 

No.  4,  SE . 

525 

i  36.5 

48.7 

133.8 

135.5 

50.8 

60.6 

60.0 

53.0 

45. 1 

35  3 

No.  5,  SE . 

Mount  Airy: 

725 

‘36.0 

133.6 

134.9 

51.0 

61.2 

65.4 

68.2 

67.0 

60.9 

53.4 

45.9 

36. 2 

51.1 

No.  1,  base  station,  eleva- 

tion  1,340 . 

41.4 

39.3 

44.7 

56.9 

66.2 

72.0 

74.9 

73.3 

5a  9 

48.2 

38.7 

56.  3 

No.  2,  W . 

160 

67.9 

41.4 

1  39.3 

45.0 

57.6 

67.8 

73.2 

75.7 

60.2 

49.8 

39.2 

57.  4 

No.  3,  E . 

73.4 

160 

41.5 

39.4 

44.9 

57.0 

66.7 

72.2 

74.8 

59. 1 

48.9 

39.3 

57.  0 

No.  4,  summit . 

67.4 

360 

41.0 

39.1 

44.4 

57.3 

67.2 

72.4 

75.0 

73.4 

59.7 

49.4 

38.6 

57.1 

No.  1,  base  station,  eleva- 

tion  2,970 . 

37. 5 

34.6 

38.8 

50.5 
51.2 

51.6 
50.5 

59.4 

60.8 

61.0 

60.6 

65.3 

66.0 

66.5 

65.8 

68.7 

68.5 

69.1 

68.4 

67.4 

67.6 

67.8 

67.6 

60.8 

60.6 

61.8 

61.6 

No.  2,  W . 

150 

37.4 

.34.6 

38.6 

38.5 

136.1 

51.4 

51.8 

No.  3,  W . 

300 

37. 1 

34.7 

134.2 

d*<.  5# 

No.  4,  summit . 

450 

135.6 

53.7 

44.3 

Tryon: 

No.  1,  base  station,  eleva- 

tion  950 . 

44.9 

43.8 

48.3 

58.7 

61.6 

6a  5 
70.6 
69.0 
67.2 

74.8 
75.4 

73.8 

71.8 

77.7 

78.6 

76.5 

74.6 

76.6 

76.9 

75.2 

73.5 

69.8 

71.1 

69.1 
67.5 

62.4 

63.6 

61.3 

60.4 

50.8 

54.4 

52.4 
51.0 

42.8 
44.0 
42.1 

40.8 

60.0 

61.4 

59.6 

58.0 

No.  2,  SE . 

380 

46.0 

45.1 

49.7 

No.  3,  SE . 

570 

45. 1 

43.8 

47.9 

59.8 

No.  4,  SE . 

1,100 

43.4 

42.0 

46.2 

58.0 

Wilkesboro: 

No.  1,  base  station,  eleva- 

tion  1,240 . 

41.6 

40.0 

45.5 

57.0 

66. 1 

72.4 

75.5 

73.  8 

67  0 

59.2 

59.4 

59.9 

59.4 

48.3 
49.2 

50.4 

50.5 

39.0 

38.9 

40.0 

39.6 

57.1 

57.6 

58.0 

57.8 

No.  2,  N . 

150 

42.2 

40.4 

45.8 

58.1 

67.6 

72.7 

75.8 

74.2 

67. 1 

No.  3,  N . 

350 

42.8 

40.9 

46. 1 

58.2 

68.0 

72.7 

75.7 

74.  0 

67.4 

No.  4,  W . 

430 

42.4 

40.2 

45.5 

58.2 

67.5 

72.6 

75.6 

74.2 

67.2 

1 3-year  average. 


*  2-year  average. 


Rate  of  decrease  in  monthly  and  annual  mean  temper¬ 
ature  on  six  selected  long  slopes. — In  Table  4a  are  brought 
together  the  six  places  having  stations  on  slopes  with  a 
difference  in  elevation  of  1,000  feet  or  more  between  the 
lowest  and  highest,  the  monthly  and  annual  values  being 
given  for  these  stations,  together  with  the  rate  of  decrease 
in  mean  temperature  with  elevation. 

Altapass,  with  a  rate  of  decrease  of  1°  for  323  feet  of 
elevation,  is  the  only  one  that  shows  a  decrease  approach¬ 
ing  the  usual  rate  in  free  air.  The  stations  at  Altapass 
are,  of  course,  on  a  regular  slope  with  station  No.  1 
several  hundred  feet  above  the  valley  floor.  On  this 


account,  during  nights  of  inversion  the  summit  station 
is  seldom  warmer  than  No.  1,  the  thermal  belt  usually 
not  reaching  the  more  elevated  sections,  as  on  most  of 
the  other  slopes.  On  some  of  these  long  slopes  the 
night  inversions  are  sufficiently  pronounced  to  make  the 
average  monthly  and  annual  values  at  the  summit 
higher  than  at  the  base. 

Thus  Cane  River  shows  a  decrease  in  mean  temper¬ 
ature  at  the  rate  of  only  1°  for  each  11,000 2  feet, 
Ellijay  for  each  1,257  feet,  Tryon  for  each  550  feet; 
while  at  Globe  and  Gorge,  the  mean  temperature  is 
actually  greatest  at  the  summit. 


54 


SUPPLEMENT  NO.  19. 


Table  4a. — Monthly  and  annual  mean  temperatures  on  the  six  long  slopes ,  showing  rate  of  increase  or  decrease  with  elevation,  1913-1916. 


[The  slopes  selected  for  this  comparison  have  a  difference  in  elevation  of  1,  000  feet  or  more  between  the  base  and  summit  station.  The  difference  in  temperature  between  the 
base  and  summit  stations  on  each  slope  is  given,  as  well  as  the  difference  in  feet  for  each  degree  difference  in  temperature.] 


Slopes  and  stations. 

Elevation.1 

Janu¬ 

ary. 

Febru¬ 

ary. 

March. 

April. 

May. 

June. 

July. 

August. 

Sep¬ 

tember 

Octo¬ 

ber. 

Novem¬ 

ber. 

Decem¬ 

ber. 

Annual 

Base. 

Summit. 

Feet. 

Feet. 

2,230 

39.6 

38.4 

41.4 

55.1 

64.2 

69.0 

72.3 

71.3 

64.6 

57.4 

47.9 

38.5 

54.9 

1,000 

36.4 

35.2 

38.0 

52.0 

61.0 

65.8 

69. 1 

68.2 

62.0 

54.6 

45.2 

35.3 

51.8 

-3.2 

-3.2 

-3.4 

-3. 1 

-3.2 

-3.2 

-3.2 

-3.1 

-2.6 

-2.8 

-2.7 

-3.2 

-3.1 

312 

312 

294 

323 

312 

312 

312 

323 

385 

357 

370 

312 

323 

2,650 

38. 5 

36.2 

38.3 

51.0 

60.8 

66.4 

69.8 

69.4 

62.5 

53.9 

43.3 

35.4 

52.  1 

1,100 

36.7 

35.0 

36.2 

52.0 

63.0 

67.0 

69.6 

68.4 

62.0 

54.2 

45.6 

35.0 

52.0 

—  1.8 

-1.2 

-2. 1 

+  1.0 

+2.2 

+  0.6 

-0.2 

-1.0 

-0.5 

+0.3 

+2.3 

-0.4 

-0  1 

611 

917 

524 

1,100 

.500 

1,833 

5,500 

1,100 

2,200 

3,667 

478 

2,750 

2 11,000 

Ellijay  No.  1 . 

2,240 

41.0 

39.4 

41.5 

54.2 

63.2 

68.3 

71.4 

70.8 

64.8 

56.4 

46.3 

38.6 

54.7 

1,760 

39.5 

37.6 

38.7 

53.7 

63.5 

66.8 

68.8 

68.4 

63.3 

56.3 

46.6 

36. 1 

53.3 

—  1.5 

—  1.8 

-2.8 

-0.5 

+0.3 

-1.5 

-2.6 

-2.3 

-1.4 

-0.1 

+0.3 

-2.5 

—1.4 

Feet  for  1°  difference.2 . 

1,173 

978 

629 

3,520 

5,867 

1,173 

677 

765 

1,257 

17,600 

5,867 

704 

1,257 

Globe  No.  1 . 

1,625 

41.0 

39.5 

43.8 

55.0 

64.8 

70.1 

73.2 

72.2 

65.9 

58.4 

47.6 

38.7 

55.8 

1,000 

41.0 

39.2 

43.5 

56.7 

66.8 

70.6 

73.3 

71.9 

65.6 

58.5 

49.0 

38.3 

56.  2 

0.0 

-0.3 

-0.3 

+  1-7 

+2.0 

+0.5 

+0. 1 

-0.3 

-0.3 

+0.1 

+1-4 

-0.4 

+0.4 

Feet  for  1°  difference.2 . 

3,333 

3,333 

588 

500 

2, 000 

10,000 

3,333 

3,333 

10,000 

714 

2,500 

2, 500 

1,400 

40.5 

39.6 

44.7 

55.5 

65.2 

70.5 

73.8 

72.7 

66.0 

58.2 

46.9 

37.7 

55.  9 

1,040 

40.8 

39.6 

43.7 

57.3 

67.0 

70.8 

73.5 

72.0 

65.6 

58.3 

48.6 

38.7 

56.3 

Difference . 

+  0.3 

0.0 

—1.0 

+  1.8 

+  1.8 

+0.3 

-0.3 

-0.7 

-0.4 

+0. 1 

+  1.7 

+  1.0 

+  0.  4 

Feet  for  1°  difference.2 . 

3,467 

1,040 

578 

578 

3,467 

3,467 

1,486 

2,600 

10, 400 

612 

1,040 

2,600 

Tryon  No.  1 . 

950 

44.9 

43.8 

48.3 

58.7 

68.5 

74.8 

77.7 

76.6 

69.8 

62.4 

50. 8 

42.8 

60.0 

Trvon  No.  4 . 

1,100 

43.4 

42.0 

46.2 

58.0 

67.2 

71.8 

74.6 

73.5 

67.5 

60.4 

51.0 

40.8 

58.0 

Difference . 

—1.5 

—1.8 

-2.1 

-0.7 

-1.3 

-3.0 

-3.1 

-3.1 

-2.3 

-2.0 

+0.2 

-2.0 

-2.0 

Feet  for  1°  difference  2 . 

733 

611 

524 

1,571 

846 

367 

355 

355 

478 

550 

5,500 

550 

550 

1  Base  station  above  sea-level;  summit  above  base. 

2  The  datum  “  Feet  for  1  degree  difference”  obviously  fails  of  any  physical  significance  when  the  temperature  differences  between  slope  stations  are  quite  small. — Ed. 


Monthly  and  annual  mean  temperature  at  the  two 
stations  having  respectively  the  highest  and  lowest  eleva¬ 
tions. — In  a  comparison  between  the  station  having 
the  lowest  altitude  above  sea  level,  the  base  station 
No.  1  in  the  valley  floor  at  Tryon,  with  an  elevation 
of  950  feet  and  a  mean  temperature  of  60°,  and  the 
most  elevated  station,  Highlands  No.  5,  with  an  eleva¬ 
tion  of  4,075  feet  above  sea  level  and  a  mean  of  51.1°, 
we  find  for  this  difference  in  elevation  of  3,125  feet  a 
difference  in  mean  temperature  for  the  entire  period 
of  8.9°,  which  is  equivalent  to  a  decrease  of  1°  for  each 
351  feet,  as  shown  in  Table  4b. 


Table  4b. — Monthly  and  annual  mean  temperatures  at  stations  having 
the  highest  and  lowest  elevations,  respectively ,  showing  the  rate  of  de¬ 
crease  with  elevation,  1913-1916. 


Stations. 

Eleva¬ 

tion. 

Jan¬ 

uary. 

Feb¬ 

ruary. 

March. 

April. 

May. 

June. 

Tryon,  No.  1 . 

Highlands,  No.  5 . 

Difference . 

Feet. 

950 

4,075 

44.9 

36.0 

-8.9 

351 

43.8 

33.6 

-10.2 

306 

48.3 

34.9 

-13.4 

233 

58.7 

51.0 

-7.7 

406 

68.5 

61.2 

-7.3 

428 

74.8 

65.4 

-9.4 

332 

Number  feet  for 
ference . 

1°  dif- 

Stations. 

Eleva¬ 

tion. 

July. 

August. 

Sep¬ 

tember. 

Octo¬ 

ber. 

Novem¬ 

ber. 

Decem¬ 

ber. 

Annual. 

Feet. 

Tryon,  No.  1 . 

950 

77.7 

76.6 

69.8 

62.4 

50.8 

42.8 

60.1 

Highlands,  No.  5. . . 

4,075 

68.2 

67.0 

60.9 

53.4 

45.9 

36.2 

51.0 

Difference . 

-9.5 

-9.6 

-8.9 

-9.0 

-4.9 

-6.6 

-9.1 

Number  feet  for  1° 

difference . 

329 

326 

351 

347 

63S 

473 

332 

THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 

INVERSIONS. 


Topographical  and  meteorological  factors  in  inversions. — 
Inversions,  which  are  primarily  radiation  phenomena, 
arc,  of  course,  most  frequent  during  clear  or  partly 
cloudy  nights.  A  low  fog  often  covers  the  valleys,  in 
which  case  the  inversions  continue  till  the  fog  is  lifted  or 
dissipated.  A  calm  or  no  more  than  a  light  wind  is  essen¬ 
tial  on  the  valley  floor,  but  a  moderate  or  brisk  southerly 
wind  at  the  higher  elevations  does  not  prevent  inver¬ 
sions,  but  may  actually  increase  the  degree  considerably, 
as  will  be  shown  later,  such  a  wind  being  characteristic 
of  the  Cyclonic  or  Overflow  Type.  The  largest  individual 
inversions  occur  when  a  high  centered  to  the  east  and 
southeast  of  the  region  is  followed  by  a  rapid  recovery 
from  low  temperature.  This  is  especially  characteristic 
of  the  Intermediate  Type,  when  a  tendency  to  rising 
temperature  is  generally  shown  at  the  higher  levels  at 
an  earlier  hour  than  on  the  valley  floor,  or  when  the  tem¬ 
perature  on  the  valley  floor  is  still  falling. 

The  factors  which  in  varying  combinations  are  most 
effective  in  causing  inversions  may  be  divided  into  two 
classes,  topographical  and  meteorological,  the  former, 
of  course,  being  absolutely  essential  as  a  foundation 
upon  which  the  meteorological  conditions  may  work. 

The  topographical  features  may  be  stated  as  follows: 
Variation  in  the  conditions  in  the  valley  floor,  whether 
flat  or  inclined,  broad  or  narrow,  open  or  inclosed;  the 
direction,  steepness,  height,  and  uniformity  of  slope;  the 
surface  area  of  the  slope  itself,  with  special  reference  to  that 
of  the  summit,  whether  a  knob,  ridge,  or  plateau;  location 
and  character  of  opposing  slopes,  if  any;  general  mass  of 
mountains  in  the  immediate  vicinity;  density  or  lack  of 
vegetal  cover  and  forest  growth;  and,  finally,  the  eleva¬ 
tion  above  sea  level. 

The  meteorological  factors  are  the  state  of  weather  as 
to  cloudiness  and  precipitation ;  the  direction  and  velocity 
of  wind;  absolute  humidity;  relative  humidity,  especially 
when  the  dewpoint  is  likely  to  be  reached;  position  of 
the  high  and  low  pressure  areas;  and  the  length  of  the 
night. 

We  might  go  through  the  entire  list  of  groups  of  sta¬ 
tions  used  in  this  research,  noting  the  individual  charac¬ 
teristics  of  the  slopes  upon  which  the  stations  are  located 
and  find  that  no  two  are  alike.  These  slopes  of  varying 
topography  furnish  many  complications  in  the  study, 
as  each  factor  is  important  and  affects  the  loss  of  heat  by 
radiation  in  a  more  or  less  degree.  The  variation  is  in 
itself  helpful,  as  it  adds  to  the  scope  and  value  of  the 
research. 

A  large  number  of  tables  and  graphs  have  been  pre¬ 
pared  in  addition  to  those  already  discussed  with  a  view 
of  covering  the  various  features  of  the  phenomenon  of 
inversion  in  a  comprehensive  manner,  and  an  examina¬ 
tion  of  these  now  follow. 

Selected  months  of  inversions,  on  the  long  slope  at  Ellijay 
and  on  the  short  slope  at  Highlands. — Table  5,  which  shows 
the  daily  minimum  temperatures  at  Ellijay,  the  longest 
slope  employed  in  the  research,  for  May,  1914,  together 
with  general  weather  conditions,  illustrates  a  period  with 
marked  inversions  occurring  almost  continually  through¬ 
out  the  month,  there  being  only  three  nights  on  which 
inversions  did  not  occur,  the  5th,  8th,  and  9th.  For  this 
month  as  a  whole  the  minima  at  stations  Nos.  4  and  5, with 
elevations  of  1,240  and  1,760  feet,  respectively,  above  the 
base,  average  8.3°  and  8°  higher  than  at  the  base  station. 
Moreover,  on  two  nights,  the  21st  and  29th,  the  minimum 
at  No.  5  was  18°  higher  than  at  the  base.  On  the  5th  and 
9th  there  are  norms  to  approximately  adiabatic  condi¬ 


tions,  the  minima  steadily  decreasing  from  the  base  to  the 
summit,  station  No.  5  reading  on  the  5th  and  9th  6°  and 
7°,  respectively,  below  the  minima  at  the  base.  On  the 
8th  the  difference  was  only  4°,  and,  while  on  the  18th  the 
minimum  at  the  summit  station  was  1°  lower  than  at  the 
base,  there  was  a  slight  inversion  shown  at  the  interme¬ 
diate  stations  on  the  slope.  The  total  monthly  precipita- 
tation  was  0.89  inches,  rain  being  recorded  on  only  six 
days.  The  weather  was  mostly  clear  throughout  the 
nionth,  with  but  few  instances  of  cloudiness.  The  largest 
inversions  occurred  with  light  winds  from  the  northwest  to 
southwest.  On  the  nights  when  no  inversions  were  noted 
either  the  weather  was  partly  cloudy  or  cloudy  or  the 
wind  was  moderate  to  brisk. 

These  large  inversions  on  the  long  slope  at  Ellijay  dur¬ 
ing  May,  1914,  were  even  exceeded  in  range  on  the  short 
slope  in  the  Waldheim  orchard  at  Highlands,  15  miles 
distant,  as  shown  in  Table  6.  A  comparison  is  here 
afforded  of  the  conditions  on  the  longest  slope,  Ellijay, 
1,760  feet,  and  on  one  of  the  shortest  slopes,  the  Waldheim 
orchard,  400  feet.  The  average  difference  for  the  month 
in  minima  between  Nos.  3  and  5,  the  base  and  summit 
stations  in  the  Waldheim  orchard,  is  9.9°,  as  compared 
with  the  difference  of  8.3°  between  Nos.  1  and  4  at  Ellijay, 
the  latter,  1,240  feet  above  the  base  and  520  feet  below 
the  summit,  marking  the  center  of  the  thermal  belt.  On 
individual  nights  the  inversions  at  Highlands  exceeded  in 
amount  those  at  Ellijay  by  as  much  as  10°,  as,  for  in¬ 
stance,  on  the  night  of  the  22d,  when  the  minima  at  Nos.  3 
and  5  in  the  Waldheim  orchard  were,  respectively,  31° 
and  56°,  a  difference  of  25°  in  400  feet,  and  those  at  Elli¬ 
jay  Nos.  1  and  4,  41°  and  56°,  respectively,  a  difference 
of  15°  in  1,  240  feet.  Moreover,  inversions  of  20°  or  over, 
occurred  in  the  Waldheim  orchard  on  four  nights,  with  a 
maximum  difference  of  25°  on  the  22d,  as  noted  above, 
while  at  Ellijay  there  were  no  inversions  over  20°,  the 
greatest  being  18°. 

The  month  of  May,  1914,  from  the  standpoint  of 
inversions  was,  of  course,  most  unusual,  there  being  a 
larger  number  during  that  month  than  in  any  other 
month  of  the  entire  period  of  the  research,  with  the 
single  exception  of  November,  1913,  when  unfortunately 
Ellijay  station  No.  5  was  not  in  operation. 

No  less  remarkable  than  the  comparison  of  inver¬ 
sions  at  Ellijay  and  Highlands  for  May,  1914  (Tables  5 
and  6),  is  that  for  these  same  slopes  during  November, 
1914,  included  in  Tables  7  and  8.  While  the  number  of 
nights  with  inversions  on  the  Ellijay  slope  is  not  so 
large  in  the  latter  month,  still  the  degree  of  individual 
inversions  is  greater,  as  well  as  the  average  degree. 
There  were  inversions  November  7  and  25  of  23°  and  21°, 
respectively,  between  the  base  and  summit,  the  first 
named  exceeding  the  May  ,  record  by  5°.  The  week 
from  the  1st  to  the  7th  of  November,  1914,  is  probably 
one  of  the  best  periods  of  continous  inversion  weather  of 
any  autumn  during  the  research. 

The  inversion  conditions  on  the  Highlands  slope  in 
November,  1914,  were  even  more  pronounced  than  in 
the  previous  May  at  that  place  as  regards  both  fre¬ 
quency  and  range,  and  it  is  probable  that  in  no  other 
period  on  any  slope  employed  in  this  research  were  they 
so  marked.  On  only  one  night  was  the  minimum  at 
No.  5  lower  than  at  the  base  station,  No.  3,  and  on  one 
night  the  minima  were  the  same  at  both  stations.  On 
the  other  28  nights  there  were  inversions  of  greater  or 
less  degree  between  the  base  and  the  summit.  In¬ 
cluding  all  30  nights,  the  average  at  No.  5  exceeded 


56 


SUPPLEMENT  NO.  19. 


that  at  No.  3  by  11°.  There  were  six  nights  with 
differences  exceeding  20°.  An  inversion  of  25°  was 
registered  on  this  slope  on  the  7th,  the  same  night  an 
inversion  of  23°  was  observed  on  the  long  slope  at 
Ellijay.  While  these  figures  for  Higlands  concern  Nos.  3 
and  5  only,  with  a  difference  in  elevation  of  400  feet,  the 
inversions  on  this  slope  are  often  seen  to  be  quite  pro¬ 
nounced  as  low  as  No.  4,  which  is  only  200  feet  above 
the  base.  The  greatest  inversion  at  that  point  in  No¬ 
vember,  1914,  was  20°  on  the  3d.  However,  occasionally 
when  small  inversions  are  noted  at  No.  5,  the  minima 
are  seen  to  be  somewhat  lower  at  No.  4  than  at  No.  3. 
The  large  inversions  on  the  short  slope  at  Highlands  are 
mostly  due  to  the  unusually  low  minima  registered  in 
the  frost  pocket  at  No.  3  and  to  the  fact  that  No.  5  is 
located  just  below  a  small  knob  with  no  opposing  slope 
close  by,  so  that  at  that  level  the  amount  of  air  free 
available  for  interchange  is  limitless.  The  degree  of  in¬ 
version  at  Ellijay  is  naturally  not  so  great  as  at  High¬ 
lands,  partly  because  of  the  higher  readings  at  the  base 
station  of  the  former. 

The  large  number  of  inversions  during  the  months  of 
May  and  November,  1914,  is  due  to  the  settled  weather 
conditions  with  clear  skies,  light  wind,  little  precipita¬ 
tion,  and  low  absolute  humidity;  and  these  conditions 
are  in  strong  contrast  to  those  of  the  month  of  July,  1916. 
At  Ellijay  (see  Table  9)  small  inversions  occurred  during 
that  month  in  the  lower  levels  between  Nos.  1  and  2  on 
13  nights  and  between  Nos.  1  and  4  and  between  Nos.  1 
and  5  on  but  9  and  7  nights,  respectively.  The  weather 
was  unusually  cloudy  and  rainy,  with  but  eight  clear 
days,  and  a  total  precipitation  of  13.71  inches,  an  un¬ 
usual  record  for  a  summer  month.  For  the  entire  month 
the  minimum  at  the  base  station,  No.  1,  averaged  the 
highest  of  the  five  stations,  2.9°  higher  than  the  summit 
station,  No.  5,  while  in  the  month  of  November,  1914 
(see  Table  7),  No.  1  averaged  8.8°  lower  than  the  summit 
station.  Summer  inversions  are  mostly  of  the  Anti- 
cyclonic  Type  and  are  ordinarily  as  frequent  as  those  of 
spring  and  autumn,  but  much  smaller  in  range  on  ac¬ 
count  of  the  high  humidity  and  cloudiness.  The  month 
of  July,  1915,  with  more  settled  weather,  in  contrast  to 
July,  1916,  was  characterized  by  frequent  inversions,  as 
shown  by  the  conditions  prevailing  at  Ellijay  (Table  10). 
Inversions  were  noted  in  that  month  every  night  be¬ 
tween  stations  Nos.  1  and  2,  on  29  nights  between  Nos.  1 
and  4,  and  on  28  nights  up  to  the  level  of  No.  5.  For  the 
entire  month  No.  1  averaged  the  lowest,  while  the  highest 
average  was  at  No.  4,  4.7°  higher  than  No.  1. 

Winter  inversions  resemble  somewhat  in  range  and 
development  those  of  spring  and  autumn,  but  the  degree 
of  inversion  is  more  fully  under  the  control  of  passing 
weather  than  at  any  other  time  of  the  year.  All  three 
types  are  found  in  that  season,  but  the  Cyclonic  Type  is 
by  far  the  most  prevalent.  During  the  colder  months 
well  developed  periods  of  inversion  are  usually  of  short 
duration  and  relatively  infrequent,  but  individual  cases 
offer  most  interesting  studies 

Inversions  in  the  winter  months  are  shown  fairly  well 
by  Tables  11  and  12,  for  the  months  of  January,  1916, 


and  February,  1915,  respectively,  at  Ellijay.  The  in¬ 
versions  were  larger  and  more  frequent  in  the  selected 
February  than  in  January,  conditions  in  the  former 
month  being  more  settled  and  permitting  inversions  of  the 
Anticyclonic  or  Ideal  Type  on  several  days  in  succession. 
On  17  nights  in  the  February  month  the  center  of  the 
thermal  belt  reached  on  this  slope  up  to  station  No.  4, 
the  average  excess  at  stations  Nos.  5  and  4  over  the  base 
station  for  the  month  being,  respectively,  2.3°  and  3.8°. 
The  largest  inversion  was  16°  on  the  13th.  In  January, 
1916,  the  inversions  were  much  less  frequent  and  less 
pronounced,  and  were  largely  of  the  Recovery  and  Cy¬ 
clonic  Types.  The  largest  inversions  were  noted  at  Nos. 
3  and  4,  with  excesses  over  No.  1  of  10°  and  12°,  respec¬ 
tively,  the  greatest  excess  at  No.  5  over  No.  1  being  9°  on 
the  4th.  During  this  month  No.  5  averaged  0.4®  lower 
than  the  base  station  and  on  only  nine  nights  did  the 
upper  station  average  higher  than  the  base. 

Tables  5  to  12,  inclusive,  embracing  data  for  the 
slopes  at  Ellijay  and  Highlands,  serve  to  especially 
illustrate  the  phenomenon  of  inversion  in  the  mountain 
region,  and  Tables  11  and  12  will  be  used  later  in  con¬ 
nection  with  the  discussion  of  norms. 

Table  5. —  Monthly  record  of  minimum  temperatures ,  daily  precipita¬ 
tion,  wind  direction  and  force,  and  state  of  weather,  May,  1914  ( selected 
month  showing  large  inversions),  Ellijay. 


[The  differences  between  the  readings  at  the  base  and  the  respective  slope  stations  may 

be  seen  by  inspection.] 


Date. 

Temperature. 

Precipitation  at  6 

p.  m.  (inches). 

Wind. 

State  of  weather. 

Station  1,  base. 

Station  2,  N., 
310.1 

Station  3,  N., 
620.1 

Station  4,  N., 
l,240.i 

Station  5,  sum¬ 

mit,  1,760.1 

Sunrise. 

Sunset. 

Previous 

night. 

Day. 

Dir. 

Force. 

Dir. 

Force. 

1.... 

40 

41 

43 

46 

47 

0.00 

w. 

Mod. . 

w. 

Mod... 

Clear. . . . 

Clear. 

2.... 

37 

39 

44 

46 

45 

0.00 

w. 

.  ..do... 

sw. 

.  ..do... 

. .  .do . 

Do. 

3.... 

41 

45 

49 

50 

50 

0.00 

sw. 

.  ..do... 

sw. 

.  ..do... 

. .  .do . 

Do. 

4.... 

54 

55 

56 

55 

54 

0.11 

sw. 

...do... 

sw. 

.  ..do... 

Cloudy. . 

Cloudy. 

5.... 

59 

58 

57 

54 

53 

0.43 

w. 

.  ..do... 

nw . 

.  ..do... 

. .  .do . 

Pt.  clay. 

6.... 

48 

53 

57 

56 

53 

O.OC 

nw. 

.  ..do... 

nw. 

.  ..do... 

Clear. . . . 

Clear. 

7.... 

45 

47 

50 

53 

53 

0.05 

w. 

.  ..do... 

sw. 

.  ..do... 

. .  .do . 

Pt.  cldy 

8.... 

47 

47 

47 

43 

43 

0. 13 

w. 

Brisk.. 

nw. 

Brisk.. 

Pt.  cldy. 

Clear. 

9.... 

45 

42 

41 

39 

38 

0.01 

nw. 

.  ..do... 

nw. 

.  ..do... 

. . .do . 

Do. 

10.... 

35 

37 

41 

44 

46 

0.0C 

w. 

Mod... 

w. 

Mod... 

. . .do . 

Do. 

11.... 

44 

49 

54 

59 

57 

0.00 

w. 

...do... 

w. 

.  ..do... 

. . .do . 

Do. 

12.... 

49 

54 

58 

62 

59 

O.OC 

w. 

...do... 

sw. 

.  ..do... 

. . .do . 

Do. 

13.... 

54 

54 

57 

59 

57 

O.OC 

sw. 

.  ..do... 

sw. 

.  ..do... 

. . .do . 

Do. 

14.... 

45 

48 

48 

47 

50 

0.00 

w. 

.  ..do... 

w. 

Brisk.. 

. . .do . 

Do. 

15.... 

39 

4(J 

43 

44 

41 

O.OC 

w. 

...do... 

w. 

Mod... 

. .  .do . 

Do. 

16.... 

39 

42 

46 

48 

47 

0.00 

w. 

...do... 

w. 

...do... 

. .  .do . 

Do. 

17.... 

42 

46 

48 

52 

5C 

0.0C 

n. 

...do... 

ne. 

.  ..do... 

...do . 

Pt.  cldy. 

18.... 

49 

51 

51 

51 

48 

0.0C 

ne. 

Brisk.. 

ne. 

Brisk.. 

. .  .do . 

Clear. 

19.... 

34 

40 

46 

45 

45 

O.OC 

n. 

Mod... 

nw. 

...do... 

. .  .do . 

Do. 

20.... 

35 

39 

44 

5C 

5C 

O.OC 

nw. 

...do... 

nw. 

Mod... 

...do . 

Do. 

21.... 

36 

42 

47 

53 

54 

0.0C 

w. 

...do... 

w. 

...do... 

. .  .do . 

Do. 

22.... 

41 

46 

51 

56 

57 

0.00 

n. 

...do... 

w. 

...do... 

. .  .do . 

Do. 

23.... 

44 

49 

53 

6C 

56 

0.  0( 

w. 

...do... 

sw. 

.  ..do... 

. .  .do . 

Do. 

24.... 

49 

53 

56 

62 

62 

0.  00 

w. 

...do... 

w. 

Lt.... 

. .  .do . 

Do. 

25.... 

49 

55 

59 

62 

59 

O.OC 

w. 

...do... 

w. 

Mod... 

. . .do . 

Do. 

26.... 

46 

50 

55 

58 

59 

0.0C 

w. 

...do... 

w. 

...do... 

. .  .do . 

Do. 

27.... 

54 

58 

59 

61 

62 

0.02 

w. 

...do... 

nw. 

.  ..do... 

. . .do . 

Pt.  cldy. 

28.... 

5C 

52 

56 

59 

63 

0.  01 

W. 

...do... 

w. 

...do... 

. . .do . 

Clear. 

29.... 

50 

55 

6C 

66 

68 

0.  15 

SW. 

...do... 

se. 

Brisk.. 

. . .do . 

Pt.cldy. 

30.... 

56 

58 

61 

64 

65 

0.00 

s. 

...do... 

s. 

Mod... 

. .  .do. . . . 

Do. 

31.... 

55 

57 

61 

65 

66 

0.00 

sw. 

...do... 

sw. 

...do... 

Clear. . . . 

Do. 

Sum. 

1,411 

1,  502 

1,598  1,669 

1, 657 

0.  89 

Mean 

45.5 

48.5 

51.5  53.8 

53.5 

1  Direction  of  slope  and  elevation  of  station  above  base  station. 


Mod. —moderate;  It.— light;  pt. —partly. 


THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 


Table  6  —Monthly  record  of  minimum  temperatures,  daily  precipita¬ 
tion  wind  direction  and  force,  and  state  of  weather,  May,  1914  (selected 
month  showing  large  inversions),  Waldheim  orchard,  Highlands 

[The  differences  between  the  readings  at  the  base  and  the  respective  slope  stations  may 

be  seen  by  inspection.]  J 


Temperature. 

Wind. 

State  of  weather. 

a5 

Date. 

CO 

c3 

rO 

H 

GO 

W 

CO 

si 

a,- 

O  ^ 

O 

Sunrise. 

Sunset. 

CO 

S 

’+> 

a  8 
.2  ^ 

cd  8 
.2  ^ 

Dir. 

Force. 

Dir. 

Force. 

Previous 

night. 

Day. 

t- 

02 

02 

CO 

Ph 

1 . 

34 

38 

38 

0.00 

se. 

Mod . 

se. 

Lt . 

Clear. . . . 

..  .do . 

...do . 

Cloudy. . 

Clear. 

Do. 

Cloudy. 

Do. 

2 . 

29 

42 

42 

0.00 

se. 

Lt . 

Calm.... 

Lt . 

...do . 

3  . 

4  . 

37 

53 

47 

52 

46 

52 

0.00 

0.00 

se. 

se. 

...do . 

...do . 

se. 

se. 

5 . 

55 

53 

54 

0.00 

nw. 

Mod . 

nw. 

Mod . 

. .  .do..... 

Pt.  cldy. 
Clear. 

Pt.  cldy. 
Do. 

6 . 

52 

53 

54 

1.  67 

nw. 

Brisk.... 

nw. 

Lt . 

Clear. . . . 

. .  .do . 

7 . 

39 

50 

51 

0.00 

nw. 

Mod . 

se. 

...do . 

8 . 

44 

43 

43 

0.00 

nw. 

Brisk. . . . 

nw. 

Brisk.... 

Cloudy. . 

9 . 

39 

38 

37 

0.00 

nw. 

. . .do . 

Calm.. . . 

. . .do . 

Do. 

10 . 

27 

40 

43 

0.00 

nw. 

Lt . 

Clear. . . . 

. . .do . 

Clear. 

Do. 

11 . 

37 

53 

53 

0.00 

nw. 

...do . 

...do . 

12 . 

45 

57 

57 

0.00 

nw. 

...do . 

...do . 

. . .do . 

Do. 

13 . 

51 

55 

55 

0.00 

nw. 

...do . 

nw. 

Lt . 

...do . 

Pt.  cldy. 

14 . 

47 

47 

51 

0.00 

nw. 

...do . 

nw. 

. .  .do . 

...do . 

Clear. 

15 . 

40 

39 

39 

0.00 

nw. 

. .  -do . 

se. 

. .  .do . 

. .  .do . 

Do. 

Pt.  cldy. 

16 . 

34 

45 

45 

0.00 

se. 

...do . 

se. 

.. -do . 

. . .do . 

17 . 

35 

47 

48 

0.00 

se. 

. .  .do . 

Calm. . . . 

. . .do . 

Cloudy. 
Pt.  cldy. 

Do. 

Clear. 

Do. 

18 . 

43 

45 

46 

0.00 

se. 

Mod . 

Cloudy. . 

19 . 

37 

44 

44 

0.00 

se. 

Brisk.... 

se. 

Lt . 

20 . 

27 

48 

48 

0. 00 

se. 

Lt . 

21 . 

28 

45 

50 

0.00 

nw. 

. .  .do _ 

nw. 

Lt . 

...do . 

22 . 

31 

51 

56 

0. 00 

nw. 

...do . 

Calm. . . . 

...do . 

Do. 

23 . 

43 

54 

53 

0.00 

nw. 

...do . 

se. 

Lt . 

. . .do . 

Do. 

24 . 

42 

56 

60 

0.00 

se. 

...do . 

nw. 

...do . 

...do . 

Do. 

25 . 

46 

55 

56 

0.00 

se. 

. . .do . 

se. 

. .  .do . 

...do . 

Do. 

26 . 

37 

51 

52 

0.00 

se. 

...do . 

se. 

...do . 

. .  .do . 

Do. 

27 . 

53 

59 

58 

0.00 

nw. 

...do . 

se. 

...do . 

...do . 

Pt.  cldy. 

28 . 

41 

54 

59 

0.00 

nw. 

...do . 

Calm.... 

...do . 

Clear. 

29 . 

44 

65 

64 

0.29 

nw. 

...do . 

. .  .do . 

. .  .do . 

Pt.  cldy. 

30 . 

53 

60 

61 

0.00 

nw. 

. . .do . 

Cloudy.. 

Do. 

Cloudy. 

31 . 

49 

61 

62 

0.00 

nw. 

. . .do . 

nw. 

Mod . 

Sum.. 

1,272 

1,  547 

1,577 

1. 96 

Mean. 

41.0 

49.9 

50.9 

1  Direction  of  slope  and  elevation  of  station  above  base  station. 

Mod.=moderate;  lt.=light;  pt.=partly. 


Table  7. —  Monthly  record  of  minimum  temperatures,  daily  precipita¬ 
tion,  wind  direction  and  force  and  state  of  weather,  November,  1914 
( selected  month  showing  large  inversions)  Ellijay. 

[  The  differences  between  the  readings  at  the  base  and  the  respective  slope  stations 
may  be  seen  by  inspection.] 


Temperature. 

CO 

4->  . 

Wind. 

State  of  weather. 

q5 

to 

£ 

£ 

£ 

a 

d  a 

CD 

d  ^ 

!i 

Sunrise. 

Sunset. 

Date. 

rO 

“8 

•* 

<N  A 

eo--*. 

tO  t'* 

c3 

Previous 

Day. 

fl 

§5 

08 

c  0 
+3 

<3 

02 

a 

d  ^ 

p<  a 

night. 

o3 

c n 

02 

o5 

CO 

ca  d 

02 

■§  p. 

M 

P‘4 

Dir. 

Force. 

Dir. 

Force. 

1.... 

26 

32 

35 

43 

44 

0.00 

w. 

Lt . 

w. 

Lt . 

Clear. . . . 

Clear. 

2.... 

29 

35 

42 

47 

45 

0.00 

w. 

. .  .do... 

w. 

..  .do... 

. . .do . 

Do. 

3.... 

33 

38 

43 

48 

49 

0.00 

w. 

. .  .do... 

w. 

. .  .do... 

. .  .do . 

Do. 

4.... 

35 

42 

47 

53 

50 

0.00 

w. 

. .  .do... 

w. 

..  .do... 

. . .do . 

Do. 

5.... 

33 

40 

48 

50 

46 

0.00 

w. 

Mod... 

w. 

Mod... 

. . .do . 

Do. 

6.... 

27 

33 

39 

45 

45 

0.00 

w. 

Lt . 

w. 

Lt . 

...do . 

Do. 

7.... 

30 

38 

43 

50 

53 

0.00 

w. 

Mod... 

w. 

Mod... 

. .  .do . 

Do. 

8.... 

40 

47 

50 

49 

49 

0. 34 

w. 

.  ..do... 

w. 

.  ..do... 

. .  .do . 

Cloudy. 

9.... 

35 

35 

35 

35 

34 

0.61 

nw. 

.  ..do... 

nw. 

...do... 

Cloudy.. 

Clear. 

10.... 

22 

22 

25 

28 

27 

0.00 

w. 

Lt.... 

w. 

Lt. . . . 

Clear. . . . 

Do. 

11.... 

25 

30 

35 

38 

39 

0.00 

w. 

. .  .do... 

w. 

.  ..do... 

. .  .do . 

Do. 

12.... 

25 

30 

33 

42 

43 

0.00 

w. 

...do... 

w. 

Brisk. 

...do . 

Do. 

13... 

34 

38 

40 

43 

43 

0.00 

sw. 

.  ..do... 

sw. 

Lt.... 

. .  .do . 

Cloudy. 

14.... 

37 

39 

46 

48 

48 

0.  25 

se. 

Brisk. 

se. 

Brisk. 

Pt.cldy. 

Do. 

15.... 

51 

49 

51 

50 

51 

0.55 

s. 

Mod... 

s. 

Mod... 

Cloudy.. 

Do. 

16.... 

42 

39 

35 

37 

35 

0.03 

w. 

Brisk. 

nw. 

...do... 

. .  .do . 

Clear. 

17.... 

15 

14 

14 

15 

13 

0.00 

nw. 

Mod... 

nw. 

...do... 

Clear. . . . 

Do. 

18.... 

14 

15 

19 

21 

20 

0.  00 

w. 

.  ..do... 

w. 

...do... 

...do . 

Do. 

19... 

22 

22 

25 

26 

25 

0.00 

w. 

.  ..do... 

w. 

...do... 

. .  .do . 

Do. 

20.... 

7 

4 

4 

1 

0 

0.18 

nw. 

Brisk. 

n. 

Brisk. 

Cloudy.. 

Do. 

21.... 

10 

8 

10 

13 

14 

0.00 

nw. 

.  ..do... 

nw. 

...do... 

Clear. . . . 

Do. 

22.... 

21 

28 

31 

29 

30 

0.00 

nw. 

Lt.... 

nw. 

Lt .... 

...do . 

Do. 

23.... 

17 

23 

26 

28 

28 

0.00 

w. 

Mod... 

w. 

Mod... 

...do . 

Do. 

24. . . . 

16 

21 

26 

30 

31 

0.00 

w. 

Lt.... 

w. 

Lt .... 

...do . 

Do. 

25.... 

19 

24 

29 

37 

40 

0.00 

w. 

...do... 

w. 

...do... 

..  .do . 

Do. 

26 

26 

31 

34 

40 

44 

0.00 

w. 

.  ..do... 

w. 

...do... 

...do . 

Do. 

27 

30 

35 

39 

44 

46 

0.00 

w. 

...do... 

w. 

...do... 

...do . 

Cloudy. 

28... 

35 

39 

45 

44 

40 

0.00 

se. 

Brisk. 

se. 

High.. 

Cloudy.. 

Do. 

29... 

48 

45 

42 

42 

42 

1.80 

se. 

High.. 

se. 

. .  .do.. . 

...do . 

Do. 

30.... 

54 

52 

50 

50 

48 

0. 52 

s. 

Brisk. 

s. 

Mod... 

...do . 

Do. 

„  ,n 

1,122 

Sum. 

37.1 

Mean 

28. 6 

i  Direction  of  slope  and  elevation  of  station  above  base  station. 

Mod.=moderate;  It. -light;  pt.=partly. 


Table  8  —Monthly  record  of  minimum  temperatures,  daily  precipita¬ 
tion,  wind  direction  and  force,  and  state  of  weather,  November,  1914 
( selected  month  showing  large  inversions),  Waldheim  orchard,  Highlands. 

[The  differences  between  the  readings  at  the  base  and  the  respective  slope  stations 
may  be  seen  by  inspection.] 


Date. 

Temperature. 

Precipitation  at  6 

p.  m.  (inches). 

Wind. 

State  of  weather. 

Station  3,  base.' 

Station  4,  SE., 

200.1 

W 

02 

a  8 

.0  ^ 

c3 

-M 

02 

Sunrise. 

Sunset. 

Previous 

night. 

Day. 

Dir. 

Force. 

Dir. 

Force. 

1 . 

19 

33 

36 

0.00 

nw. 

Lt . 

se. 

Lt  . 

2 . 

33 

40 

38 

0.00 

nw. 

. . .do . 

nw. 

...do . 

. .  .do . 

Do. 

3 . 

25 

45 

48 

0.00 

nw. 

. .  .do . 

nw. 

. .  .do . 

. .  -do . 

Do. 

4 . 

31 

49 

48 

0.00 

nw. 

. .  .do . 

Calm.... 

. .  .do . 

Do. 

5 . 

32 

46 

46 

0.00 

nw. 

Brisk. . . 

nw. 

Brisk . . . 

. .  .do . 

Do. 

6 . 

33 

41 

41 

0.  00 

Lt 

Lt 

Do 

7 . 

25 

43 

50 

0.00 

nw. 

. .  .do . 

nw. 

. .  .do . 

. .  .do . 

Do. 

8 . 

35 

45 

47 

0. 55 

nw. 

. .  .do . 

se. 

. . .do . 

. .  .do . 

Cloudv. 

9 . 

34 

34 

32 

0.00 

nw. 

. .  .do . 

nw. 

. .  .do . 

. .  .do . 

Pt.  cldy 

10 . 

17 

24 

30 

0.00 

nw. 

. .  .do . 

se. 

. . .do . 

Cloudy.. 

Clear. 

11 . 

22 

32 

38 

0.00 

nw. 

. .  .do . 

nw. 

. .  .do . 

Clear. . . . 

Do. 

12 . 

18 

33 

42 

0.00 

se. 

. .  .do . 

se. 

. .  .do . 

. .  .do . 

Do. 

13 . 

33 

40 

44 

0.  00 

se. 

. .  .do . 

Calm.... 

. .  .do . 

Cloudy. 

14 . 

30 

43 

51 

2.18 

se. 

Mod . 

se. 

Mod . 

Cloudy.. 

Do. 

15 . 

50 

49 

56 

0.  60 

se. 

..  .do . 

se. 

Lt . 

. .  .do . 

Do. 

16 . 

37 

33 

39 

0.00 

nw. 

. .  .do . 

nw. 

Brisk.... 

. .  .do . 

Clear. 

17 . 

13 

13 

17 

0.00 

nw. 

Lt . 

Lt . 

Do. 

18 . 

7 

17 

23 

0.00 

se. 

. .  .do . 

Calm. . . . 

. .  .do . 

Do. 

19 . 

19 

21 

27 

0.00 

nw. 

Mod . 

se. 

Mod . 

. .  .do . 

Pt.  cldy. 

20 . 

1 

0 

1 

0.  00 

nw. 

High. . . . 

Lt. 

Do. 

21 . 

10 

7 

13 

0.00 

nw. 

Brisk.... 

se. 

. .  .do . 

Clear. . . . 

Clear. 

22 . 

28 

27 

32 

0.00 

nw. 

. .  .do . 

nw. 

. .  .do . 

. .  .do . 

Do. 

23 . 

27 

26 

29 

0.00 

nw. 

. .  .do . 

se. 

...do . 

. .  .do . 

Do. 

24 . 

10 

23 

30 

0.00 

nw. 

. .  .do . 

se. 

...do . 

. .  .do . 

Do. 

25 . 

28 

29 

39 

0.00 

Calm.. . . 

se. 

. .  .do . 

Do. 

26 . 

36 

36 

44 

0.00 

se. 

Lt . 

Do. 

27 . 

25 

40 

49 

0.00 

se. 

...do . 

se. 

Lt . 

. .  .do . 

Cloudy. 

28 . 

38 

44 

48 

0.  40 

se. 

. .  .do . 

se. 

High.... 

Cloudv.. 

Do. 

29 . 

38 

38 

45 

4.00 

se. 

High.... 

se. 

Brisk.... 

. .  .do . 

Do. 

30 . 

46 

45 

50 

0.  20 

Lt . 

Do. 

800 

996 

1,123 

7.93 

26.7 

33.2 

37.7 

1  Direction  of  slope  and  elevation  of  station  above  base  station. 

Mod.=moderate;  It. —light;  pt. —partly- 


Table  9. — Monthly  record  of  minimum  temperatures,  daily  precipita¬ 
tion,  wind  direction  and  force,  and  state  of  weather,  July,  1916  ( selected 
month  showing  practically  no  inversions),  Ellijay. 

[The  differences  between  the  readings  at  the  base  and  the  respective  slope  stations  may 

be  seen  by  inspection.] 


Date. 

Temperature. 

Precipitation  at  6 
p.  m.  (inches). 

Wind. 

State  of  weather. 

Station  1,  base. 

Station  2,  N., 
310. 1 

Station  3,  N., 
620. 1 

Station  4,  N., 
1,240.1 

Station  5,  sum¬ 
mit,  l,760.i 

Sunrise. 

Sunset. 

Previous 

night. 

Day. 

Dir. 

Force. 

Dir. 

Force. 

1  .  .  . 

58 

62 

61 

62 

63 

1.15 

Calm.. 

nw. 

Lt.... 

Clear. .. . 

Pt.  cldy. 

2.. . 

61 

63 

61 

61 

61 

.02 

. .  .do... 

nw. 

...do... 

Pt.cldy. 

Clear. 

3... 

61 

63 

60 

59 

58 

.00 

w. 

Lt.... 

nw. 

...do... 

. . .do . 

Do. 

4.  .  . 

60 

62 

62 

64 

62 

.00 

w. 

...do... 

w. 

...do... 

Clear. . . . 

Do. 

5.. . 

58 

60 

60 

61 

59 

.00 

w. 

Mod... 

nw. 

...do... 

. .  .do . 

Do. 

6. .  . 

59 

62 

61 

62 

60 

.00 

w. 

Lt . 

sw. 

...do... 

. . .do . 

Pt.  cldy. 

7. .  . 

63 

63 

60 

60 

58 

.06 

s. 

...do... 

s. 

.  ..do... 

Cloudy.. 

Cloudy. 

8.. . 

62 

62 

59 

58 

56 

1.05 

se. 

Mod... 

se. 

...do... 

. .  .do . 

Do. 

9. . . 

64 

64 

61 

61 

59 

1.68 

se. 

.  ..do... 

se. 

Mod... 

. .  .do . 

Do. 

10.. . 

64 

65 

61 

61 

59 

.85 

s. 

.  ..do... 

s. 

Lt . . . . 

. .  .do . 

Do. 

11.. . 

69 

65 

62 

61 

59 

.16 

s. 

...do... 

s. 

...do... 

...do . 

Do. 

12. 

65 

62 

61 

62 

59 

.75 

s. 

Lt . . . . 

s. 

...do... 

. .  .do — . 

Clear. 

13. . . 

65 

63 

62 

64 

61 

.02 

s. 

..  .do... 

s. 

...do... 

Pt.  cldy. 

Pt.  cldy. 

14.  . 

63 

60 

59 

62 

60 

.03 

se. 

...do... 

se. 

...do... 

...do . 

Do. 

15. . . 

69 

64 

62 

62 

61 

.30 

s. 

. .  .do... 

s. 

...do... 

Cloudy.. 

Cloudy. 

16. 

72 

67 

65 

65 

63 

1.68 

s. 

. .  .do... 

sw. 

...do... 

...do . 

Do. 

17 

67 

64 

63 

65 

63 

.01 

Calm. . 

sw. 

...do... 

. .  -do . 

Do. 

18 

61 

62 

61 

64 

63 

.83 

s. 

Lt.... 

s. 

Mod... 

Pt.cldy. 

Pt.  cldy. 

19. . . 

63 

62 

60 

62 

61 

1.50 

s. 

...do... 

s. 

...do... 

Cloudy.. 

Cloudy. 

20. . . 

62 

62 

61 

62 

61 

.26 

sw. 

...do... 

sw. 

Lt . . . . 

...do . 

Do. 

21. 

64 

63 

62 

63 

60 

.68 

s. 

...do... 

sw. 

...do... 

...do . 

Do. 

22. 

66 

64 

64 

63 

61 

.76 

Calm. . 

sw. 

...do... 

...do . 

Do. 

23 

61 

60 

59 

61 

60 

.00 

sw. 

Lt.... 

s. 

...do... 

...do . 

Pt.  cldy. 

24. .  . 

60 

59 

60 

62 

61 

.45 

s. 

. .  .do... 

s. 

...do... 

Clear.... 

Do. 

25 

60 

61 

59 

60 

59 

1.03 

s. 

...do... 

sw. 

...do... 

..  .do . 

Do. 

26. . 

58 

60 

59 

62 

59 

.00 

s. 

.  ..do... 

sw. 

...do... 

Pt.cldy. 

Do. 

27 

58 

58 

56 

59 

58 

.16 

s. 

...do... 

se. 

...do... 

...do . 

Do. 

?8 

60 

60 

60 

60 

59 

.15 

Calm.. 

s. 

...do... 

...do . 

Clear. 

29 

65 

66 

64 

65 

62 

.13 

s. 

Lt.... 

se. 

Mod... 

Clear.... 

Pt.  cldy. 

30 

65 

66 

63 

63 

61 

.00 

e. 

...do... 

e. 

..  .do... 

Pt.cldy. 

Clear. 

31U 

62 

64 

62 

64 

62 

.00 

e. 

...do... 

e. 

Lt . . . . 

Clear.... 

Do. 

Sum. 

1,945 

1,938 

1,890 

1,920 

13.71 

Mean 

62.7 

62.5 

61.0 

61.9 

59.8 

- - 

1  Direction  of  slope  and  elevation  of  station  above  base  station. 

Mod.-moderate;  Lt.=  light;  Pt.=partly. 


58 


SUPPLEMENT  NO.  19. 


Table  10. — Monthly  record  of  minimum  temperatures,  daily  precipita¬ 
tion,  ivind  direction  and  force,  and  state  of  weather,  July,  1915  ( selected 
month  showing  typical  summer  inversions),  Ellijay. 

[The  differences  between  the  readings  at  the  base  and  the  respective  slope  stations  may 

be  seen  by  inspection.] 


Date. 

Temperature. 

Precipitation  at  6 
p.  m.  (inches). 

Wind. 

State  of  weather. 

Station  1,  base. 

Station  2,  N., 
310.1 

Station  3,  N., 
620.1 

Station  4,  N., 
1,240.1 

Station  5,  sum¬ 
mit,  1,760.1 

Sunrise. 

Sunset. 

Previous 

night. 

Day. 

Dir. 

Force. 

Dir. 

Force. 

1... 

56 

58 

58 

59 

57 

0. 16 

w. 

Mod... 

w. 

Mod... 

Cloudy.. 

Cloudy. 

2... 

56 

57 

55 

56 

55 

0. 40 

w. 

...do... 

w. 

. .  .do... 

Pt.  cldy. 

Clear. 

3.. 

55 

58 

58 

60 

58 

0. 08 

w. 

...do... 

w. 

...do... 

Cloudy.. 

Cloudy. 

4.. 

59 

61 

60 

60 

59 

0. 35 

sw. 

...do... 

sw. 

..  .do... 

. .  -do . 

Do. 

5.. 

61 

63 

60 

59 

58 

1.22 

sw. 

. .  .do... 

w. 

..  .do... 

. . .do . 

Do. 

6.. 

47 

51 

51 

52 

52 

0.01 

nw. 

...do... 

nw. 

..  .do... 

Pt.  cldy. 

Clear. 

7... 

51 

56 

56 

58 

56 

0. 00 

vv. 

.  ..do... 

w. 

.  ..do... 

Clear. . . . 

Do. 

8... 

61 

65 

65 

65 

63 

0.07 

nw. 

.  ..do... 

nw. 

. .  .do... 

Cloudy.. 

Cloudy. 

9.. 

54 

59 

58 

61 

61 

0.00 

w. 

...do... 

w. 

.  ..do... 

Clear.... 

Pt.  cldy. 

10... 

59 

62 

60 

61 

60 

0.  62 

w. 

...do... 

w. 

...do... 

. .  .do . 

Do. 

11..  . 

5S 

61 

60 

60 

59 

0.00 

nw. 

...do... 

nw. 

.  ..do... 

. .  .do . 

Clear. 

12..  . 

61 

66 

67 

67 

64 

0.00 

nw. 

.  ..do... 

nw. 

.  ..do... 

. .  .do . 

Do. 

13..  . 

61 

65 

64 

65 

63 

0.  04 

w. 

...do... 

w. 

...do... 

Pt.  cldy. 

Pt.  cldy. 

14.  .  . 

56 

60 

60 

62 

62 

1.01 

sw. 

. .  .do... 

sw. 

Brisk.. 

Clear. . . . 

Do. 

15... 

60 

62 

61 

63 

63 

0.65 

w. 

. .  .do... 

w. 

Mod... 

...do . 

Cloudy. 

16..  . 

59 

63 

62 

64 

65 

0.00 

w. 

...do... 

w. 

...do... 

. .  .do . 

Clear. 

17.. . 

58 

63 

64 

66 

63 

0.00 

w. 

. .  .do... 

w. 

.  ..do... 

.  ..do . 

Do. 

18.. 

58 

62 

62 

65 

63 

0.  00 

w. 

...do... 

w. 

.  ..do... 

. . .do . 

Do. 

19. .  . 

60 

64 

63 

66 

66 

0.  06 

w. 

...do... 

w. 

.  ..do... 

. .  .do . 

Cloudy. 

20.. . 

60 

63 

63 

66 

64 

0.13 

w. 

.  ..do... 

w. 

...do... 

. . .do . 

Pt.  cldy. 

21.. . 

55 

59 

58 

60 

57 

0.00 

w. 

. .  .do... 

w. 

...do... 

. . .do . 

Clear. 

22.. . 

50 

53 

53 

54 

52 

0. 76 

w. 

...do... 

w. 

...do... 

...do . 

Pt.cldy. 

23... 

48 

50 

50 

53 

52 

0.00 

ne. 

...do... 

w. 

...do... 

...do . 

Clear. 

24... 

51 

54 

54 

56 

55 

0. 00 

nw. 

...do... 

nw. 

. .  .do... 

. . .do . 

Do. 

25... 

53 

56 

57 

59 

5S 

0. 02 

w. 

.  ..do... 

w. 

..  .do... 

..  .do . 

Do. 

26.. 

56 

58 

58 

61 

60 

0.03 

ne. 

..  .do... 

ne. 

.  ..do... 

...do . 

Do. 

27... 

57 

58 

59 

62 

62 

0. 00 

nw. 

.  ..do... 

nw. 

..  .do... 

. . .do . 

Do. 

28.. . 

59 

60 

61 

66 

65 

0. 00 

w. 

...do... 

w. 

...do... 

. .  .do . 

Do. 

29... 

60 

61 

64 

66 

63 

0.00 

w. 

...do... 

w. 

...do... 

.  ..do . 

Do. 

30..  . 

60 

62 

63 

68 

65 

0.00 

w. 

.  ..do... 

w. 

.  ..do... 

...do . 

Do. 

31.. . 

61 

62 

64 

68 

69 

0.00 

w. 

...do... 

w. 

...do... 

...do . 

Do. 

Sum. 

1,760 

1,852 

1,848 

1,906 

1,869 

5.61 

Mean 

56.8 

59.7 

59.6 

61.5 

60.3 

. 

1  Direction  of  slope  and  elevation  of  station  above  base  station. 


Mod.  =  moderate;  Lt.  =  light;  Pt.  ■=■  partly. 

Table  11 . — Monthly  record  of  minimum  temperatures,  daily  precipita¬ 
tion,  wind  direction  and  force  and  state  of  weather,  January,  1916, 
(. selected  month  showing  typical  winter  inversions),  Ellijay. 

[The  differences  between  readings  at  base  and  the  respective  slope  stations  may  be 

seen  by  inspection.] 


Temperature. 

CO 

Wind. 

State  of  weather. 

, 

to 

c« 

£ 

£ 

£ 

a- 

gfl 

Sunrise. 

Sunset. 

Date. 

-o 

2s 

Vs  w 

d 

o 

a  2 

O  CO 

d 

o 

•'f  o 
dc$ 

to1'- 

d"l 

in 

•Bv 

Previous 

night. 

Day. 

■4-» 

*-£ 

Dir. 

Force. 

Dir. 

Force. 

c3 

03 

03 

05 

*  a 

m 

02 

02 

02 

02 

h, 

1.. . 

44 

44 

41 

43 

41 

0.15 

w. 

Mod... 

sw. 

Mod... 

Cloudy. . 

Pt.cldy. 

2..  . 

54 

57 

55 

57 

53 

0. 12 

w. 

.  ..do... 

w. 

.  ..do... 

.  ..do . 

Cloudy. 

3..  . 

31 

35 

36 

38 

37 

0.00 

nw. 

.  ..do... 

nw. 

.  ..do... 

Clear. . . . 

Clear. 

4..  . 

20 

23 

29 

26 

29 

0.00 

w. 

.  ..do... 

w. 

.  ..do... 

.  ..do . 

do 

5..  . 

28 

33 

34 

38 

36 

0.00 

w. 

Brisk  . 

sw. 

.  ..do... 

Pt.  cldy. 

Cloudy. 

6..  . 

48 

47 

47 

48 

44 

0. 67 

sw. 

Mod.  . 

sw. 

.  ..do... 

Cloudy.. 

do 

7..  . 

49 

48 

49 

47 

44 

0.  96 

w. 

.  ..do... 

w. 

.  ..do... 

. .  .do . 

do 

8..  . 

35 

36 

32 

33 

32 

0.00 

nw. 

.  ..do... 

nw. 

.  ..do... 

.  ..do . 

Clear. 

9..  . 

29 

27 

24 

25 

27 

0.00 

nw. 

.  ..do... 

nw. 

.  ..do... 

Clear. . . . 

do 

10... 

28 

30 

29 

30 

28 

0.03 

w. 

...do... 

w. 

.  ..do... 

Cloudy.. 

Cloudy. 

11..  . 

48 

49 

48 

49 

45 

0.  05 

w. 

.  ..do... 

w. 

.  ..do... 

.  ..do . 

do 

12..  . 

53 

55 

54 

53 

49 

0.09 

w. 

.  ..do... 

sw. 

Brisk.. 

.  ..do . 

do 

13.. . 

45 

43 

40 

39 

37 

0.51 

sw. 

Brisk  . 

w. 

Mod... 

.  ..do . 

Clear. 

14..  . 

23 

23 

20 

18 

21 

0.  00 

w. 

Mod.. . 

w. 

.  ..do... 

Pt.  cldy. 

Do. 

15... 

25 

26 

26 

23 

22 

0.00 

sw. 

...do... 

sw. 

.  ..do... 

Cloudy. 

Cloudy. 

16.. . 

33 

31 

30 

29 

27 

0.  17 

w. 

.  ..do... 

w. 

.  ..do... 

. . .do . 

Do. 

17.. . 

15 

13 

10 

8 

5 

0.00 

nw. 

Brisk  . 

w. 

.  ..do... 

. . .do . 

Clear. 

18... 

8 

7 

5 

7 

8 

0.00 

nw. 

Mod... 

nw. 

.  ..do... 

Clear. . . . 

Do. 

19.. . 

10 

12 

10 

13 

15 

0.00 

w. 

.  ..do... 

w. 

.  ..do... 

Pt.cldy. 

Do. 

20..  . 

22 

25 

24 

26 

27 

0.00 

w. 

.  ..do... 

s. 

.  ..do... 

Clear. .”. . 

Do. 

21..  . 

33 

39 

43 

45 

41 

0.24 

sw. 

.  ..do... 

sw. 

.  ..do... 

Cloudy. . 

Cloudy. 

22. .  . 

51 

50 

48 

48 

43 

1.  14 

sw. 

Gale. . 

nw. 

.  ..do... 

. . . do . 

Do. 

23..  . 

29 

32 

32 

35 

35 

0.00 

nw. 

Mod. . 

nw. 

Brisk.. 

Clear. .. . 

Clear. 

24..  . 

24 

29 

30 

33 

32 

0.00 

w. 

.  ..do... 

w. 

Mod.. . 

.  ..do . 

Do. 

25..  . 

35 

39 

39 

41 

41 

0.00 

sw. 

.  ..do... 

s. 

...do... 

Pt.  cldy. 

Cloudy. 

26... 

49 

50 

48 

49 

47 

0. 10 

s. 

.  ..do... 

s. 

.  ..do... 

Cloudy*. . 

Pt.  cldy. 

27..  . 

51 

52 

50 

50 

47 

0.22 

s. 

.  ..do... 

s. 

. .  .do... 

. .  .do . 

Cloudy. 

28..  . 

49 

53 

52 

52 

49 

0.04 

sw. 

...do... 

sw. 

...do... 

. .  .do . 

Do. 

29..  . 

51 

53 

52 

53 

50 

0.  02 

sw. 

.  ..do... 

sw. 

.  ..do... 

. .  .do . 

Do. 

30..  . 

53 

53 

50 

50 

47 

0.00 

s. 

.  ..do... 

s. 

. .  .do... 

. .  .do . 

Do. 

31... 

56 

55 

52 

50 

47 

0. 10 

sw. 

Brisk . 

sw. 

Brisk  . 

. .  .do . 

Do. 

Sum. 

1,129 

1,172 

1,139 

1, 168  1, 116 

4.61 

Mean 

36.4 

37.8 

36.7 

37.7 

36.0 

1  Direction  of  slope  and  elevation  of  station  above  base  station. 


Mod. "-moderate;  Lt.=light;  Pt.  =  partly. 


Table  12. —  Monthly  record  of  minimum  temperatures,  daily  precipita¬ 
tion,  wind  direction  and  force,  and  state  of  weather,  February,  1915, 
(selected  month  showing  typical  winter  inversions),  Ellijay. 

[The  differences  between  readings  at  base  and  the  respective  slope  stations  may 

be  seen  by  inspection.] 


Date. 

Temperature. 

Precipitation  at  6 

p.  m.  (inches). 

Wind. 

State  of  weather. 

Station  1,  base. 

Station  2,  N., 

310.1 

Station  3,  N., 

620.1 

Station  4,  N., 

1,240A 

Station  5,  sum¬ 

mit,  1.760.1 

Sunrise. 

Sunset. 

Previous 

night. 

Day. 

Dir. 

Force. 

Dir. 

Force. 

1.. . 

55 

52 

52 

50 

48 

1.93 

s. 

High.. 

s. 

Mod. . 

Cloudy. . 

Cloudy. 

2.. . 

35 

39 

39 

40 

38 

0.  13 

sw. 

Mod. . 

w. 

Brisk.. 

. . .do . 

Do. 

3.. . 

29 

28 

26 

24 

22 

0.  70 

nw. 

.  ..do... 

n. 

Mod. . 

.  ..do . 

Do. 

4..  . 

20 

23 

22 

26 

24 

0.00 

nw. 

.  ..do... 

nw. 

.  ..do... 

Clear. . . . 

Clear. 

5.. . 

29 

33 

32 

34 

32 

0. 35 

w. 

.  ..do... 

s. 

.  ..do... 

Cloudy. . 

Cloudy. 

6..  . 

29 

38 

36 

33 

32 

0.00 

w. 

.  ..do... 

w. 

.  ..do... 

.  ..do . 

Clear. 

7..  . 

29 

27 

25 

23 

23 

0.00 

nw. 

Brisk . 

nw. 

...do... 

Clear. . . . 

Do. 

8..  . 

24 

24 

21 

18 

17 

0.00 

nw. 

Mod.  . 

nw. 

...do... 

.  ..do . 

Do. 

9.. . 

11 

15 

14 

19 

13 

0.00 

nw. 

.  ..do... 

nw. 

.  ..do... 

.  ..do . 

Do. 

10... 

13 

19 

21 

29 

27 

0.00 

w. 

.  ..do... 

w. 

Lt . 

.  ..do . 

Do. 

11..  . 

18 

24 

25 

29 

29 

0.00 

w. 

.  ..do... 

w. 

Mod.  . 

.  ..do . 

Do. 

12..  . 

27 

33 

34 

38 

36 

0.00 

w. 

.  ..do... 

w. 

.  ..do... 

.  ..do . 

Do. 

13..  . 

25 

32 

35 

41 

40 

0.00 

s. 

Lt.... 

s. 

Lt.... 

.  ..do . 

Pt.cldy. 

14..  . 

46 

47 

46 

43 

42 

0. 07 

s. 

Mod.  . 

s. 

Mod.  . 

. .  .do . 

Cloudy. 

15... 

48 

47 

46 

45 

42 

0.80 

s. 

.  ..do... 

s. 

.  ..do... 

Cloudy. . 

Do. 

16..  . 

29 

31 

30 

32 

30 

0.00 

w. 

Lt.... 

w. 

Lt.  ... 

Clear. . . . 

Pt.  cldy. 

17..  . 

19 

24 

24 

30 

31 

0.00 

w. 

.  ..do... 

w. 

.  ..do... 

.  ..do . 

Clear. 

18..  . 

20 

25 

27 

32 

32 

0.00 

w. 

Mod. . 

sw. 

Mod. . 

.  ..do . 

Do. 

19..  . 

22 

27 

28 

29 

29 

0.00 

w. 

...do... 

w. 

.  ..do... 

.  ..do . 

Do. 

20..  . 

21 

25 

25 

26 

26 

0.00 

w. 

.  ..do... 

w. 

.  ..do... 

.  ..do . 

Do. 

21..  . 

19 

26 

28 

31 

31 

0.00 

w. 

.  ..do... 

w. 

.  ..do... 

.  ..do . 

Do. 

22. 

40 

40 

40 

39 

38 

0.02 

s. 

. . .do. . 

s. 

Mod.  . 

Cloudy. . 

Cloudy. 

23..  . 

44 

47 

44 

42 

40 

0.  38 

s. 

Lt. ... 

s. 

Lt.  ... 

.  ..do . 

Do. 

24..  . 

42 

45 

42 

42 

41 

0.  58 

sw. 

Mod.  . 

nw. 

Mod.  . 

. . .do . 

Clear. 

25..  . 

32 

32 

29 

27 

25 

0.00 

n. 

Brisk.. 

n. 

Brisk  . 

.  ..do . 

Cloudy. 

26..  . 

20 

23 

21 

22 

20 

0.00 

nw. 

.  ..do... 

w. 

Mod.  . 

. .  .do . 

Pt.  cldy. 

27..  . 

27 

30 

28 

31 

29 

0.00 

w. 

Mod. . 

w. 

. .  .do. .. 

Clear. .. . 

Cloudy. 

28..  . 

37 

38 

35 

34 

33 

0.00 

w. 

Lt.... 

w  . 

Lt.... 

Cloudy.. 

Do. 

Sum. 

810 

894 

875 

915 

873 

4.96 

Mean 

28.9 

31.9 

31.2 

32.7 

31.2 

1  Direction  of  slope  and  elevation  of  station  above  base  station. 

Mod. =moderate;  Lt. “light;  Pt. “partly. 


Inversions  on  six  selected  long  slopes  having  a  vertical 
height  of  1,000 feet  or  more. — Table  13  shows  the  frequency 
of  inversions  in  the  individual  months  and  years  of  the 
research  on  the  six  long  slopes  having  a  vertical  height 
of  1,000  feet  or  more — Altapass,  1,000  feet;  Cane  River, 
1,100  feet;  Ellijay,  1,760  feet;  Globe,  1,000  feet;  Gorge, 
1,040  feet;  and  Tryon,  1,100  feet.  The  figures  given  in 
the  table  represent  results  shown  by  differences  between 
minima  at  stations  No.  1  and  certain  stations  higher 
up  on  the  slopes — usually  Nos.  2,  3,  and  4,  at  Altapass, 
Tryon,  and  Ellijay,  respectively,  and  the  summit  stations, 
Nos.  4,  3,  and  5,  at  Cane  River,  Globe,  and  Gorge,  re¬ 
spectively — in  each  case  the  upper  station  as  here  indicated 
being  approximately  in  the  center  of  the  thermal  belt. 
For  purposes  of  convenience  this  table  has  been  prepared 
to  embrace  all  inversions  as  low  as  5°,  and  this  is  necessary 
because  of  the  small  number  of  large  inversions  registered 
at  the  observing  stations  at  Altapass,  where  the  lowest 
station,  No.  1,  is  not  really  a  base  station,  but  rather  on 
the  slope  several  hundred  feet  above  the  valley  floor. 

The  largest  number  of  inversions  noted  in  any  one 
year  on  all  six  slopes  together  is  860  in  1913,  and  in  no 
year  did  the  number  fall  as  low  as  800.  The  largest 
number  of  inversions  on  a  single  slope  for  the  entire 
four-year  period  is  743  at  Ellijay,  which  has  the  greatest 
vertical  height,  this  being  an  average  of  186  a  year,  or 
more  than  one  every  other  day,  The  average  amount 
of  inversion  at  Ellijay  is  9°,  and  an  extreme  of  23°  was 
registered  on  both  November  13,  1913,  and  November  7, 
1914,  as  shown  by  the  differences  in  minima,  and  at  8 
a.  m.  on  those  two  dates  inversions  between  Nos.  1  and 
4  were,  respectively,  24°  and  26°,  the  former  being  the 
largest  inversions  at  any  hours  noted  at  Ellijay  during 
the  research. 

Altapass  naturally  has  the  smallest  recorded  number, 
173,  or  43  a  year,  the  average  range  of  its  inversions 


THERMAL  BELTS  AND  FRUIT 

being  6  .  On  the  iUtapass  slope  the  greatest  inversion 
based  upon  the  minima,  13°,  was  observed  February  18, 
1915,  while  on  that  day  a  difference  of  19°  was  noted 
between  Nos.  1  and  3  at  7  a.m. 

All  the  data  in  Table  13  are  based  upon  observations 
o  minimum  temperature  and  do  not  necessarily  show 
special  instances  of  inversion  at  any  particular  hour  on 
any  one  night,  as  in  the  two  cases  at  Altapass  and  Elliiav 
just  referred  to.  J  J  ’ 

While  the  greatest  inversion  at  Gorge  through  a 
comparison  of  minima  is  shown  in  Table  13  to  be  24° 
there  was  actually  an  inversion  of  31°  between  Nos.  1 
and  5  on  that  slope  at  6  a.  m.  November  13,  1913,  this 
being  the  greatest  inversion  noted  on  any  slope  during 
the  period  of  the  research.  The  greatest  inversion  at 
any  horn  at  Cane  River  was  30°  at  8  a.  m.,  November  21, 
1913,  and  at  the  same  hour  January  28,  1914,  while  at 
Globe  and  Tryon  the  largest  inversion  at  any  hour  was 
26°,  which  occurred  at  8  a.  m.  on  both  November  13, 1913, 
and  February  18,  1916,  at  Globe  and  at  6  a.  m.  on  both 
November  14,  1913,  and  February  18,  1916,  at  Tryon. 
On  both  dates  at  Globe  the  maximum  inversion  was  be¬ 
tween  the  base  and  summit  stations,  while  at  Tryon  on 
the  November  date  the  inversion  occurred  between  Nos. 
1  and  3,  and  on  the  date  in  February  between  Nos.  1  and 
2.  Gorge,  Cane  River,  and  Tryon  have  individual 
instances  of  inversions  of  24°,  as  shown  by  Table  13 
and  the  largest  average  amount  on  all  the  six  on  all  the 
six  slopes,  10°,  is  found  at  Gorge.  Large  inversions  at 
individual  hours  occur  quite  frequently  at  a  few  of  the 
more  elevated  stations  under  the  Intermediate  and 
Cyclonic  Types,  and  more  examples  will  be  given  in 
detail  later. 

As  may  be  seen  in  the  table,  inversions  are  usually 
most  frequent  in  the  spring  and  autumn  months,  No¬ 
vember,  May,  April,  and  October  having  the  largest 
totals  for  the  entire  period  in  the  order  given.  Ellijay, 
which  has  the  largest  number  of  inversions  on  these  six 
long  slopes,  as  stated  above,  has  a  total  of  83  in  the  four 
Novembers,  while  Cane  River  has  an  even  greater  num¬ 
ber,  87,  the  average  number  for  that  month  at  both 
places  being  21  and  22,  respectively.  Ellijay  has  its 
largest  monthly  total  In  May,  equalling  the  Cane  River 
figure  for  November,  87.  Gorge  also  has  its  largest 
number  for  the  four-year  period  in  May,  totaling  81.  On 
the  six  slopes  as  a  whole  November,  1913,  and  May,  1914, 
have  the  largest  number  for  the  individual  months, 
totaling  125  and  123,  respectively,  and  in  the  latter 
month  the  maximum  record  of  26  dates  of  inversion  was 
noted  at  Ellijay,  there  being  only  five  nights  without 
inversions  (see  Table  5).  Reference  is  made  on  a  pre¬ 
vious  page  to  July,  1915,  in  which  inversions  were  noted 
every  night  at  Ellijay,  but  that  statement  includes  all 
inversions,  even  as  small  as  1°,  while  only  inversions  no 
smaller  than  5°  are  included  in  Table  13.  May,  1915,  a 
month  with  considerable  cloudiness  and  storm  move¬ 
ment,  has  a  total  of  only  65  inversions  on  the  six  slopes, 
but  even  in  that  month  20  of  these  are  noted  at  Ellijay. 
The  month  of  August  generally  has  the  smallest  num¬ 
ber  of  inversions  of  5°  or  more,  the  four-year  total  for 
that  month  at  Cane  River  and  Ellijay  being  34  and  38, 
respectively,  while  the  least  number  in  any  one  August 
at  either  place  is  as  low  as  5.  July,  1916,  of  all  the  indi¬ 
vidual  months  during  the  four  years  of  record,  has  the 
smallest  number  of  inversions,  the  total  on  the  six  slopes 
being  only  seven,  and  of  these  one  occurred  at  Ellijay, 
none  at  Cane  River  and  Globe,  and  four  at  Tryon.  July, 
1916,  was  a  most  unusual  month  in  the  Carolina  moun¬ 
tain  region,  as  heavy  and  even  torrential  rains  were 

30442—23 - 6 


GROWING  IN  NORTH  CAROLINA. 


frequent  and  conditions  were  generally  unfavorable  for 
the  occurrence  of  inversions. 

.  November  not  only  has  the  greatest  number  of  inver¬ 
sions  on  all  six  slopes  as  a  whole,  but  it  also  has  the 
greatest  average  range,  12°,  as  compared  with  11°  for 
April,  and  10°  for  May  and  October,  and  July  and  Au¬ 
gust  have  the  smallest  range  of  inversion,  with  only  7°. 

Figure  52  is  intended  to  supplement  Table  13  and 
illustrates  graphically  the  frequency  of  inversions,  the 
average  range,  and  the  extreme  range  on  five  of  the  long 
slopes,  Altapass  being  omitted  for  obvious  reasons. 

Inversions  on  six  selected  short  slopes. — Table  14  pre¬ 
sents  inversion  data  for  the  six  short  slopes,  Blantyre, 
Blowing  Rock,  Bryson,  Hendersonville,  Highlands,  and 
Mount  Airy,  after  the  plan  of  Table  13,  which  gives  the 
data  for  the  six  long  slopes. 

The  frequency  of  inversions  of  5°  or  more  on  the  short 
slopes,  as  shown  by  Table  14,  is  much  the  same  as  on 
the  long  ones,  the  totals  for  the  entire  four-year  period 


Fig.  52.— Montlily  frequency,  average,  and  extreme  degrees  of  inversion  on  five  selected 

long  slopes. 


being,  respectively,  3,291  and  3,316,  the  difference  being 
hardly  appreciable.  Moreover,  if  Altapass  be  omitted 
from  the  list  of  long  slopes  because  of  the  fact  that  the 
absence  of  a  base  station  there  voids  the  comparison,  it 
should  be  apparent  that  the  frequency  of  these  inver¬ 
sions  of  5°  or  more  would  be  even  relatively  greater  on 
the  long  slopes. 

The  largest  number  of  inversions  noted  in  any  onp'year 
on  the  six  short  slopes  is  868  in  1913,  and  the  smallest 
number  in  any  one  year  is  778  in  1915.  The  largest 
number  of  inversions  on  a  single  slope  is  738  in  the  Wald¬ 
heim  orchard  at  Highlands,  as  compared  with  743  on 
the  long  slope  at  Ellijay  (see  Table  13).  For  the  four- 
year  period  the  largest  average  degree  of  inversion  at 
Highlands  was  11°,  as  compared  with  9°  at  Ellijay.  A 
maximum  inversion  of  27°  occurred  at  Highlands  on 
November  21,  1913,  Hendersonville  having  on  the  same 
date  an  inversion  of  25°.  The  smallest  number  of  inver¬ 
sions  on  these  short  slopes  for  the  four-year  period  is 
423  at  Mount  Airy,  while  the  smallest  average  range  is 
noted  at  Bryson,  7°. 

November  leads  in  the  number  of  inversions  of  5°  or 
more  on  the  short  slopes,  440,  by  a  considerable  margin, 
its  excess  over  the  other  months'  being  greater  than  that 


60 


SUPPLEMENT  NO.  19. 


noted  in  Table  XIII  for  the  lorm  slopes.  The  greatest 
average  range  of  inversion  is  also  in  November,  11°, 
while  May  follows  with  the  second  largest  total  of  372 
and  with  the  average  range  of  10°.  August  has  the 
smallest  total,  176,  and  the  smallest  average  range,  7°. 
These  figures  are  comparable  with  those  given  in  Table  13 
for  the  long  slopes.  There  is,  in  fact,  a  striking  similarity 
in  the  seasonable  variation  on  the  long  and  short  slopes, 
the  greatest  frequency  of  inversion  occurring  in  the 
montks  of  November,  May,  and  April,  in  the  order 
named,  and  the  least  in  August. 

Inversions  of  stated  amounts  on  six  selected  long  slopes 
in  the  year  1914 . — Table  15,  supplementing  Table  13, 
contains  inversion  data  for  the  six  long  slopes,  Altapass, 
Cane  River,  Ellijay,  Globe,  Gorge,  and  Tryon,  on  the  5° 
basis,  together  with  additional  data  for  101 2 3 * * 6,  15°,  and  20° 
for  the  year  1914.  The  figures  covering  inversions  of  5°, 
which  appear  in  Table  13  for  1914,  are  repeated  in  Table 
15  in  order  to  show  the  contrast  between  them  and  the 
arger  degrees  of  inversion.  One  year  only,  1914,  is 


used  in  this  comparison,  as  this  will  serve  just  as  well  as 
the  entire  four-year  period. 

As  should  be  expected,  the  table  shows  that  Altapass 
has  but  few  inversions  even  moderately  large,  it  having 
no  valley  floor  station  for  purposes  of  comparison.  It 
has  an  inversion  of  10°  or  more  only  twice  during  the  year, 
both  instances  occurring  in  November  (Table  15),  and 
as  its  largest  inversion  is  only  11°,  this  slope  is  not  found 
in  the  other  two  portions  of  the  table  embracing  inver¬ 
sions  of  15°  and  20°.  While  Ellijay  leads  in  the  number 
of  inversions  of  5°  or  more,  196,  and  Gorge  is  second  with 
172,  Gorge  leads  in  the  number  of  inversions  of  10°  or 
more  with  a  total  of  89,  Ellijay  following  with  a  total  of 
81.  Gorge  also  has  the  greatest  number  of  inversions 
of  15°  or  more,  with  a  total  of  33,  Ellijay  being  again 
second,  with  31,  and  in  the  number  of  inversions  of  20°  or 
more  Gorge  is  preeminently  in  the  lead,  with  a  total  of  8, 
Cane  River  following,  with  3,  and  Ellijay  and  Tyron, 
with  2  each.  Globe  does  not  appear  in  the  last  list,  as 
its  greatest  individual  inversion  is  only  17°. 


Table  13. —  Total  monthly  and  annual  number  of  inversions  of  5°  or  more  on  the  6  long  slopes  having  a  difference  in  elevation  of  1,000  feet  between  base 

and  summit  stations,  1913-1916,  inclusive. 


Stations. 


1913. 

Altapass _ 

Cane  River... 

Ellijay . 

Globe . 

Gorge . 

Tryon . . 


Total  column 
(a). 

Average  col¬ 
umn  (b). 

Greatest  c  o  1  - 
limn  (c). 


1914. 

Altapass . 

Cane  River.. 

Ellijay . 

Globe . 

Gorge . 

Tryon . 


Total  column 
(a). 

Average  col¬ 
umn  (b). 

Greatest  c  o  1  - 
umn  (c) . 


1915. 

Altapass _ 

Cane  River. . 

Ellijay . 

Globe . 

Gorge . 

Tryon . 


Total  column 
(a). 

Average  col¬ 
umn  (b). 

Greatest  c  o  1 
umn  (c). 


1916. 
Altapass .... 
Cane  River.. 

Ellijay . 

Globe . 

Gorge . 

Tryon . 


Total  column 
(a). 

Average  col 
umn  (b). 

Greatest  col 
umn  (c). 


Jan 

1 

| 

Feb. 

Mar. 

Apr. 

1 

May. 

June. 

July. 

Aug. 

Sept. 

Oct. 

Nov. 

Dec. 

Annual. 

a 

b 

C 

d 

a 

b 

c 

dj 

a 

b 

c 

d 

a 

b 

c 

d 

a 

b* 

C 

J 

a 

b 

c 

d 

a 

b 

c 

d 

a 

b 

c 

d 

a 

b 

C 

d 

a 

b 

c 

d 

a 

1 

b 

c 

d 

a 

i 

b 

c 

d 

a 

b 

c 

d 

i  4 

‘  6 

1  2 

5 

‘3 

5 

1  4 

6 

6 

6 

7 

12 

2 

5 

5 

18 

0 

0 

4 

5 

6 

5 

5 

6 

7 

25 

5 

7 

10 

27 

10 

8 

12 

21 

2 

6 

7 

16 

47 

6,12 

Nov.  21. 

'14 

‘  7 

i  7 

7 

__ 

10 

S 

13 

13 

h 

19 

16 

11 

21 

4 

.5 

9 

.8 

6 

7 

7 

.6 

19 

11 

7 

2 

4 

.3 

7 

.0 

25 

18 

11 

.9 

27 

24 

14 

23 

19 

15 

12 

19 

13 

173 

9  23 

Nov.  19. 

‘IS 

1  •') 

‘8 

5 

11 

7 

15 

10 

6 

19 

18 

11 

22 

6 

17 

8 

.4 

8 

.6 

7 

9 

8 

11 

6 

0 

5 

.5 

8 

3 

25 

17 

11 

.8 

15 

24 

15 

23 

13 

17 

11 

18 

13 

187 

9  23 

Nov.  13. 

13 

9 

15 

19 

7 

7 

10 

18 

9 

7 

12 

9 

11 

12 

7 

24 

15 

.0 

9 

5 

.5 

7 

:5 

6 

.1 

6 

9 

19 

10 

7 

9 

4 

.1 

7 

3 

24 

13 

10 

.5 

14 

23 

11 

9 

21 

14 

10 

19 

6 

152 

9 

9 

Dec.  6. 

14 

10 

14 

17 

7 

10 

LI 

17 

9 

8 

14 

9 

14 

14 

20 

24 

22 

13 

24 

5 

19 

10 

21 

4 

. 7 

8 

1 

6 

10 

8 

1 

i 

.0 

9 

:3 

27 

14 

12 

17 

15 

23 

14 

24 

21 

18 

12 

22 

13 

177 

11  24 

Nov.  21. 

17 

10 

1616 

7 

12 

22 

17 

11 

1 

16 

9 

14 

13 

21 

19 

16 

11 

20 

2 

7 

6 

8 

18 

6 

6 

7 

9 

2 

6 

7 

29 

15 

6 

9 

12 

6 

9 

13 

27 

21 

12 

24 

14 

12 

10 

17 

13 

124 

9, 

24 

Nov.  14. 

SO 

s 

-- 

- 

3S 

8 

-- 

53 

8 

- 

-• 

71 

12 

21 

19 

92 

11 

24 

5 

75 

8 

21 

14 

67 

7 

11 

6 

48 

7 

2 

4 

69 

7 

13 

11 

•73 

11 

19 

27 

*o 

2 

13 

24 

21 
l  14 

j7S 

11 

22 

13 

860 

9 

24 

/ Nov.  21  and 
\  H- 

5 

s 

9 

23 

2 

6 

7 

3 

0 

0 

1 

1 

6 

6 

22 

7 

6 

9 

26 

0 

0 

3 

5 

7 

23 

1 

5 

5 

23 

5 

6 

9 

28 

3 

7 

9 

1 

6 

8 

11 

8 

1 

5 

5 

16 

34 

6 

11 

Nov.  8. 

10 

12 

23 

>9 

9 

9 

.5 

L8 

‘  9‘S 

16 

16 

12 

9 

16 

23 

24 

11 

20 

22 

14 

8 

ii 

29 

11 

10 

16 

23 

13 

7 

9 

19 

14 

8 

12 

5 

16 

8 

18 

31 

22 

13 

20 

27 

4 

10 

14 

18 

15S 

9 

23 

Jan.  29. 

16 

11 

17 

2,8 

11 

8 

n 

18 

12 

9 

15 

16 

17 

10 

18 

22 

26 

11 

18 

21 

19 

9 

13 

29 

21 

8 

L6 

24 

11 

7 

10 

17 

16 

8 

15 

16 

18 

9 

18 

31 

21 

15 

23 

7 

8 

8 

9 

19 

196 

9 

23 

Nov.  7. 

10 

9 

13 

23 

8 

9 

13 

18 

6, 

.1 

17 

16 

9 

10 

15 

22 

21 

11 

16 

22 

14 

8 

11 

.1 

11 

10 

15 

24 

13 

7 

10 

19 

14 

8 

13 

28 

14 

7 

15 

31 

18 

10 

14 

3 

4 

5 

7 

17 

142 

9 

17 

Mar.  16. 

14 

10 

18 

29 

11 

9 

17 

18 

8 

11 

20 

16 

12 

12 

19 

23 

24 

14 

24 

22 

18 

10 

15 

25 

13 

11 

17 

24 

16 

8' 

12 

19 

15 

9 

14 

28 

15 

8 

14 

31 

20 

15 

24 

27 

6 

7 

12 

17 

172 

10 

24 

Nov.  27. 

11 

11 

22 

29 

10 

10 

16 

18 

12 

10 

21 

16 

15 

10 

17 

22 

21 

9 

19 

26 

5 

6 

8 

21 

8 

6 

8 

14 

0 

0 

•• 

15 

7 

9 

15 

10 

8 

12 

29 

18 

12 

19 

7 

2 

6 

6 

18 

127 

9 

22 

Jan.  29. 

66 

10 

23 

29 

51 

9 

17 

18 

47 

8 

21 

16 

66 

10 

19 

23 

123 

10 

24 

22 

70 

7 

15 

25 

67 

8 

17 

24 

54 

6 

12 

19 

79 

8 

15 

16 

76 

8 

18 

31 

105 

13 

24 

27 

25 

7 

14 

18 

829 

9 

24 

Nov.  27. 

2 

5 

5 

5 

4 

8 

13 

18 

0 

0 

2 

6 

8 

21 

1 

5 

5 

10 

2 

5 

5 

18 

0 

0 

2 

5 

5 

26 

7 

6 

7 

25 

6 

8 

10 

31 

11 

7 

10 

9 

4 

6 

7 

23 

41 

6 

13 

Feb.  18. 

7 

7 

10 

10 

7 

11 

20 

13 

6 

S 

13 

is 

21 

11 

24 

20 

12 

7 

9 

16 

6 

8 

11 

11 

9 

8 

io 

3C 

5 

7 

8 

24 

11 

7 

10 

27 

17 

12 

22 

1.3 

18 

10 

19 

1 

13 

8 

16 

27 

132 

9 

24 

Apr.  20. 

13 

8 

12 

14 

14 

10 

16 

1.3 

14 

8 

12 

15 

24 

12 

22 

20 

20 

8 

16 

6 

18 

7 

15 

11 

20 

6 

8 

17 

11 

7 

14 

7 

18 

8 

12 

26 

17 

10 

19 

31 

18 

12 

20 

5 

13 

9 

17 

31 

200 

9 

22 

Do. 

8 

6 

9 

16 

9 

9 

20 

13 

8 

7 

11 

15 

22 

10 

19 

20 

10 

6 

9 

16 

11 

7 

12 

11 

14 

6 

9 

31 

8 

7 

9 

7 

10 

8 

13 

25 

13 

9 

13 

29 

18 

6 

13 

2 

6 

6 

8 

27 

137 

7 

20 

Feb.  13. 

12 

f 

11 

5 

11 

10 

20 

13 

12 

9 

16 

26 

25 

12 

23 

20 

12 

9 

12 

17 

11 

8 

13 

21] 

19 

8 

12 

27 

11 

8 

12 

24 

14 

9 

13 

25 

15 

11 

18 

21 

18 

11 

18 

2 

14 

8 

12 

24 

174 

9 

23 

Apr.  20. 

12 

11 

15 

16 

13 

9 

14 

11 

8 

9 

15 

26 

21 

10 

17 

6 

10 

8 

12 

4 

4 

8 

12 

11 

8 

6 

8 

30 

2 

6 

8 

8 

8 

6 

8 

19 

6 

9 

13 

26 

21 

12 

19 

1 

13 

11 

17 

27 

126 

9 

17 

Dec.  22. 

.54 

8 

15 

| 

16 

58 

10 

20 

13 

48 

8 

16 

26 

115 

11 

24 

20 

65 

8 

16 

6 

52 

7 

15 

11 

70 

7 

12 

27 

39 

7 

14 

7 

68 

8 

13 

25 

74 

10 

22 

13 

104 

10 

20 

5 

63 

8 

17 

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8 

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Apr.  20. 

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0 

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5 

7 

11 

27 

14 

7 

4 

4 

8 

8 

11 

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C 

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7 

51 

7 

1  1 

Sept.  27. 

r. 

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12 

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15 

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7 

15 

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27 

17 

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18 

26 

17 

11 

19 

2S 

2C 

11 

19 

4 

2C 

9 

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7 

162 

9 

1! 

Nov.  4. 

si: 

2 

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11 

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16 

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11 

20 

7 

10 

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7 

9 

27 

12 

9 

16 

25 

17 

11 

10 

28 

2C 

11 

19 

11 

17 

11 

If 

7 

16C 

( 

2C 

Mav  1. 

i 

4 

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11 

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1- 

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1 

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17 

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16 

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10 

7 

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0 

4 

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S 

6 

7 

21 

12 

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10 

20 

12 

f 

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28 

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9 

i: 

11 

11 

8 

14 

7 

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8 

If 

May  10. 

.  i 

i: 

3 

1 

11 

1 1 

i.' 

li 

r 

1- 

1 

l: 

17 

2C 

i: 

22 

17 

15 

£ 

1C 

f 

S 

10 

1- 

10 

15 

25 

19 

If 

h 

:2f 

17 

i; 

19 

21 

23 

9 

17 

7 

182 

! 

21 

May  7. 

. 

l 

12- 

1 

1 

2. 

is 

ir 

i 

1 

1C 

If 

IS 

10 

IS 

If 

14 

13 

0 

1- 

s 

e 

e 

11 

12 

22 

14 

11 

i; 

if 

6 

IS 

27 

If 

11 

20 

7 

144 

9 

23 

Feb.  18. 

4 

31 

1 

6 

5  1 

12, 

51 

6, 

i 

71 

7 

5  1 

If 

10< 

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20 

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If 

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7 

10 

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19 

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h 

20 

7 

817 

9 

23 

Feb.  18. 

1  Values  interpolated. 

2  Also  Nov.  13,  1913. 

3  Also  Nov.  21,  1914. 

(a)  Number  of  nights  during  which  inversions  of  5°  or  more  occurred  between  any  two  stations  on  a  slope. 

(b)  Average  (degrees)  of  inversions. 

(c)  Amount  (degrees)  of  greatest  inversion. 

(d)  Date  of  greatest  inversion. 


THERMAL  BEL  I  S  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 


61 


TaB,-R  n-Total  monthly  andan™1  «■  "»  * i *«*  My . in *»*.*  '/(MmmiWw 

_  an<i  «u»wnU  *to/toru,  191S-19J6,  inclusive— I'ontimird. 


Stations. 


1013-1010. 

Altapass . 

Cane  Kivcr . 

Kill  I  ay . 

Clone . 

Gorge . 

Try on . 

Total,  column  (a) . . . 
Average,  column  fb> 
Greatest,  column  (c) 


Jan. 


Feb. 


It 
3* 
56 
3‘J 
31 
V,  I 


|->44 


be 


(I  9 
X23 
a  17 

8  IS 

9  18 
022 


b  c 


10  6  1.1 
36  9  20 
t:  s  n 
33  H  20 
43  10  20 
tl  1023 


Mar. 


a  b  c 

<66 

37  K  18 

45  X  IS 
3t  X  17 

46  920 
44  1021 


Apr.  May. 


b  c 


June. 


8  23  213  9  23  213  8  21 


12  6  10. 
58  1 1  24 
71  II  22 
SS  1019! 
6X  12  23 
64  12  21 


20  6  10 
73  921 
87  10  22 
63  9  19 
81  12  24 
66  9  20 


32X  11  24  390  10  24 


Oct. 


Nov 


Dee. 


163  714 


,b  c 


--  7  10 
6‘  1022 
09  10  19 
S2  x  IS 
63  I0IS 
6  12  .V,  9  13 


8  1  8  316  1022  429  12  24 


be  a  be 


31  8  12 
*7  12  21 
X3  1323 
72  9  19 
7x  13  24 
7*  : ;  24 


II  A 


61  9  2 


Four-year  annual. 


Feb.  18.  191 6. 
Apr.  30,  1913. 
Nov.  7,  1*14  » 
Feb  13  |9IS.> 
Nov.  27,  1*16 
Nov.  I«,  1*13. 


'  * 

b  c 

171 

6  13 

625 

9  24 

7*3 

92) 

549 

*  JO 

705 

10  24 

131 

9  24 

3,316 

9  24 

Table  1-1.  Total  monthly  and  annual  number  of  xnvertiont  of  5°  or  more  on  six  ihort  tlopci 


Stations. 


1913. 

Blantyre . 

Blowing  Kock.  . 

Bryson . 

Hendersonville. 

Highlands . 

Mount  Airy.... 


Total,  column 

(a) . 

Average,  col¬ 
umn  (b) . 

Greatest,  col¬ 
umn  (c) . 


Jan. 


Feb. 


e  d 


14  9  15  19 

6  6  7  16 

>8*6  ... 
*  10  >9  ..  .. 
WHO.. ... 
8  710 


53  8  15  19  40 


1914. 

Blantyre .  16  1118  29 

Blowing  Hock .  8  7  1123 

Bryson . *  18  *  7  . 

Hendersonville .  14  10is2j 

Highlands .  9  12  17  14 

Mount  Airy .  7  9  13  29 


M  1018  29  45 


Total,  column 

<») . 

Average,  col¬ 
umn  (b) _ 

Greatest,  col¬ 
umn  (c) . 

1915. 

Blantyre .  12  9  15  16 

Blowing  Kock . ]  5  5  6  14 

Bryson .  4  8 10  5 

Hendersonville .  11  8  14  14 

Highlands . >12  *  8  ..  .. 

Mount  Airy . j  3  8  9  16 

Total,  column 

<•> . ;• 

Average,  col¬ 
umn  (b) - 

Greatest,  col¬ 
umn  (c) . 

1916. 

Blantyre . 1  6 

Blowing  Hock .  6 

Bryson .  9 

Hendersonville .  7 

Highlands  .  8  10  21 

Mount  Airy .  3 

Total,  column 

(*) . :• 

Average,  col¬ 
umn  (b) 

Greatest,  col 
umn  (c) 


10 

3 

1  9  > 
1  8 
>  7 
3 


|  e  d 


Mar. 


b  c 


_ - 


11  16  18  12  915  23 
6  6  19  5  8  10  9 

*10>sL. 

*9*9  ,.|.. 
*9*8  .. 

3  7  8  9 


6  . . 

SL 

8  1019 


8  16  18  4.x  8  15  21 


14  15  2 
8  10  27 
8,10  2 
8  11  13  2 
7  10,12  27 
6  8  10  3 


1211 
4  6 


7,11 
7  7 


20  16 
7  16 


8  8  10  16 
11  9  16  16 


21  16 
10  16 


10  15  2  49  9  21  16 


44 

9  10  16  21 

8  9  14  13 
6  S  10  13 

9  II  15  13 
II)  II  2)  18 

4  7,1021 


Apr. 


a  1.  c 


12  14  21  25 
8  12  17  25 
18  9  13  24 

12  13  2)18 

13  14  22  19 


May. 


bed 


17  10  17 
13  10  14 
15  9  15 


June. 


a  bled 


July.  I  Aug. 


hbcd&bcd 


Sept. 


a  b  c 


Oct. 
a  b  c 


Nov. 


Dec. 


Nov.  It,  1*13 


Annual. 


9  8  II  H  10  6  9  18  5  5  6  28  10  6  V  25 
1  12  8  13  18  10  7  11  8  11  7 


a  b 


4  8  7  11  IS  2  10  13 
17  12  24  4  17  7  11  IS  8  6  8 
19  13  2.  4  2112  22  16  1X10  18 
9  1225  14  10  17  3  11  7  12  16  S  6  10 


V  4 


7  3  5  5  251  7  6  9  25 


09  12  22  19  95  11  25  4 


10  IS  23 
9  12  18 
8  11  24 
13  11  1828 
13  13  22  22 
6  8  12  22 


-r 


80  9  22  16  53  8  18 


24  11  16  21  16 


8  6  6  726 
8  19  9  15  5 
8  8  7  817 


13  8  13  24 


12  8  13  25 
15  13  22  24 

13  7  11  26 


13  11  16  13  25  14  21 
8  10  16  5  IV  11  18 

18  S  12  27  *2)*  12 

14  11  19  27  24  13  25 
16  13  23  6  23  16  27 
10  *15 


e  d  a  b 


15  3  18  W14 


8  52  7  15  5  70  8  22  24  81  10  23  6  128 


4  5 


6  19  14 


7  1121  13  7  12  13 

18  1018  27  9  6  8  12  15  X  12  24  12  8  15  2)14 

20  8(12  26  6  6  9  3  2  5  5  M  1  S  5  24  1 

22  12  18  23  16  8  12  29  13  8  1126  6  5  6  19  12 

2)  15  25  22  21 


"T 


13  I*  1016  13  IV.  *21  Apr  25. 

21  14  9  17  6  122  KIN  Nov  21. 

. . .  *  l«  *  1 0 .  134  6  IS  Mai  4 

21  16  10  14  17  152  9  25  Nov  21. 

21  2)  14  23  5  191  12  77]  Da 
7  14  7jl!  14  113  6  17  May  I. 


13  27  21  99  1023  5  8r.x  *27  Nov.  21 


11  8  16  I  2)  13]g 
10  8  14  22  16  9  15 

5  6  10  31  20  10  17 
13  8  1231  3)  11  IX 
16  10  17  31  22  14  25 


69  10  22  22  120  11  25  22  78, 


8]  12  15  23  11  21  2)  15  7  13  16 

7  10  16  16  9  14  27  4  6  7  16 

9  4  21  8  12  20  5  7  10  16  O 

112  29  25  11  24  2)  13  9  14  16  12 

7  II  14  21  13  25  2)  16  9  15  6  13 

6  7  26  10  8  15  26 


7  10  .113  17  168  .  Mar.  18. 

14  2  9  12  26  116  61-  Mav  27. 

26  4  6  7  16  10*  7  171  Nov  ». 

7  i  612  17  I  S3  »|6  Mav  XI. 

7  14  10  15  12  191  II  2'.  May  JB. 

3  4  911  24  115  617  Nov.  1. 


- 


7  39  6  U  12  657  *25  May  22. 


5  16  611  4  136  6  21  Apr.  30 

6  5  6  *  3|  117  7  IVi  Oct.  31 

25  116  9  4  85|  7  14  Nov.  25. 

5  14  9  12  4  162  9  24  Apr  2) 

17  9  1018  31  16510  25,  Da 

7  3  7  6  27  91  7  32-  Apr.  3». 


119  10  25  2*  61 


— u. 


15  10  17  14  20  11  16  14  19  II  2)  10  9  6  11  1 

7  6112:14  11  9  12  19  12  9  IX  7  11  6  9  14 

16  9  16  14  17  6  1210  2  6  6  2 

16  10  21  19  19  10  19  10  17  6  1510 

14  12  22  19  16  16  25  7  1  8  10  19  5 

6  6  6  21  10  8  10  10  12  6  6  5 


7  6  26  7  911  28 
7  8  19  14  6  IS  26 
2  Ml  X 
6  11  28  16  9  17  22 
6  1421  19  11  17  26 
6102614  615  26 


58  9  17  18  62  9  17  14  83  10  22  19  93  11  25  7  09  6  19  5  19  6  8  1  34  7  14  21  72  9  17  26 


16  9  14  29  16  11  16 
11  6  1.3  6  13  6  13 

10  7  12  25  19  8  15 

16  1015  13  16  1221 

16  13222>  17  II  2> 

17  8  13  1 1  i  Ml 


90  9  22  28  96  10  21 


Mar 


Apr.  ,  May. 


be  a  ,  b 


1913-1910. 

Blantyre .  ®  }} 

Blowing  Kock  .  *•  $  }* 

Bryson .  '  J 

lfendersoo  vUle .  I?  .?  i? 

Highland .  JV2?t 

Mount  Airy .  21  h  11 


b  c 


701221 
40  10  17 
72  616 
66  II  24 
64  13  25 
28  MS 


75 1021 
47  9  18 
57  6  15) 
71  11  24 
71  13  25 
51  617 


5  60  815  31  776  9  25  Apr.  20. 


21  17  919  7  1*3  *'jnJ  May  la 

II  II  7  12  7  lie  a  ia  May  7 

22  12  9  1»  17  I07|  7 IX  Dec.  IT. 

4  14  923  7  1ST  «r*  Dec  7. 

3  17  II  JO  3  171  II  35  Mar  7. 

11  11  All  4  104,  7  IV  Sept  » 


9  23  7  79*  9  25  May  7. 


Four  year  annual 


Apr  a.  i *H  * 

i  «t  31,  1915. 
Der.  17. 191* 
Sri  31.  I9U. 
Da 

Nev.  ».  1*1*. 


®2>  i»  *2.  »  »2. 3*0.025  372.025  »»  « • 

(.rosiest,  column  (e) . jl 


22  311 1021  *1011  27  241  *2)  J  2*1  * 27  Nee  II,  1915. 


(b)  Aurtp  'WrMirllattnluu  _ 

(ci  Amount  at  greatest  1**,**,>- 

d)  Date  tl  greatest  bvatka 


»  Values  Interpolated. 

'MNnte&Sttt  d'^tng  which  inversions  of  5*  or  mar,  occurred  Mean  any  two  station,  on  a  slop* 


62 


SUPPLEMENT  NO.  19 


Table  15. —  Total  monthly  and  annual  number  of  inversions  of  5°,  10°,  15 °,  and  20°  on  six  long  slopes  having  a  difference  in  elevation  of  1,000 feet 

between  base  and  summit  stations,  1914. 

INVERSIONS  OF  5°  OR  MORE. 


Stations. 

Jan. 

Feb. 

Mar. 

Apr. 

May. 

June. 

July. 

Aug. 

Sept. 

Oct. 

Nov. 

Dec. 

Annual. 

a 

b  c 

d 

a 

b 

c 

d 

a 

b 

c 

d 

5 

b 

c 

d 

a 

b 

c 

d 

a 

b 

c 

d 

a 

b 

c 

d 

a 

b 

c 

d 

a 

b 

c 

d 

a 

b 

c 

d 

a 

b 

c 

d 

a 

b 

c 

d 

a 

b 

c 

d 

Altapass . 

5 

8  9 

23 

2 

6 

7 

3 

0 

0 

1 

6 

6 

22 

7 

6 

9 

26 

0 

0 

3 

5 

7 

23 

i 

5 

5 

23 

5 

6 

9 

28 

3 

7 

9 

1 

6 

8 

11 

8 

i 

5 

5 

16 

34 

6 

11 

Nov.  8. 

Cane  River . 

10 

12  23 

29 

9 

9 

15 

IS 

1  9 

>8 

ie 

16 

12 

9 

16 

23 

24 

11 

2022 

14 

8 

ii 

29 

11 

10 

16 

23 

13 

7 

9 

19 

14 

8 

12 

5 

16 

8 

18 

31 

22 

13  20 

27 

4 

10 

14 

18 

158 

9 

23 

Jan.  29. 

Ellijay . 

16 

11 17 

28 

11 

S 

11 

18 

12 

9 

15 

16 

17 

10 

18 

22 

26 

11 

IS 

21 

19 

9 

13 

29 

21 

8 

16 

24 

11 

7 

10 

17 

16 

8 

15 

16 

18 

9 

18 

31 

21 

15  23 

7 

8 

8 

9 

19 

196 

9 

23 

Nov.  7. 

Globe” . 

10 

913 

23 

8 

9 

13 

18 

6 

11 

17 

16 

9 

10 

15 

22 

21 

11 

16 

22 

14 

8 

n 

11 

11 

10 

15 

24 

13 

7 

10 

19 

14 

8 

13 

28 

14 

7 

15 

31 

18 

10 

14 

3 

4 

5 

7 

17 

142 

9 

17 

Mar.  16. 

Gorge . 

14 

10  18 

29 

11 

9 

17 

18 

8 

11 

20 

16 

12 

12 

19 

23 

24 

14 

24 

22 

18 

10 

15 

25 

13 

11 

1724 

16 

8 

12 

19 

15 

9 

14 

28 

15 

8 

14 

31 

20 

1524 

27 

6 

7 

12 

17 

172 

10  24 

Nov.  27. 

Tryon . 

11 

1122 

29 

10 

10 

16 

18 

12 

10 

21 

16 

15 

10 

17 

22 

21 

9 

19 

26 

5 

6 

8 

21 

8 

6 

8 

14 

0 

15 

7 

9 

15 

10 

8 

12 

29 

18 

12 

19 

7 

2 

6 

6 

18 

127 

9 

22 

Jan.  29. 

Total,  column 
(a) 

1 

Average,  col- 

66 

10  23 

.  . 

51 

9 

17 

.  _ 

47 

8 

21 

.  . 

66 

10 

19 

.  . 

123 

10 

24 

.. 

70 

7 

15 

.  . 

67 

8 

17 

.. 

54 

6 

12 

79 

8 

15 

... 

76 

8 

IS 

105 

13 

24 

25 

7 

14 

.  .  . 

829 

9 

24 

Greatest,  col- 

umn  (c) . 

INVERSIONS  OF  10°  OF  MORE. 


| 

|  1 

2M 

11 

8 

2 

ion 

Nov.  8. 

Cane  River . 

7 

15 

23 

29 

2 

12 

15 

18 

2 

14 

16 

16 

5 

13 

16 

23 

16 

13  20 

22 

3 10 

11 

29 

8  12 

16 

23 

3 

11 

12 

5 

3  12 

18  31 

15 

14 

20 

27 

2 

13 

14 

18 

66 

13 

23 

Jan.  29. 

10 

13 

17 

28 

2 

11 

11 

18 

6 

13 

18 

16 

5 

16 

18 

22 

14 

14  18 

21 

9 

11 

13  29 

6  13 

16 

24 

2 

10  10 

17 

6 

12 

15 

16 

3  5 

18  31 

18 

16 

23 

7 

81 

12 

23 

4 

12 

13 

23 

5 

a 

13 

18 

4 

12 

17 

16 

5 

13 

15 

22 

11 

13 

16 

22 

3 

10 

11  11 

7  12 

15 

24 

2 

10  10 

19 

3 

11 

13 

28 

1  15 

15  31 

11 

12 

14 

3 

56 

12 

17 

Mar.  16. 

Gorge . 

6 

14 

18 

29 

5 

13 

17 

18 

3 

16 

20 

16 

8 

14 

19 

23 

20 

15 

24 

22 

12 

12 

15 

25 

8  14 

17 

24 

3 

12 

12 

19 

5 

13 

14 

28 

1 14 

14  31 

17 

16 

24 

27 

”i 

12 

12 

17 

89 

14 

24 

Nov.  27. 

6 

15 

22 

29 

5 

13 

16 

18 

5 

15 

21 

16 

7 

13 

17 

22 

8 

13 

19 

26 

2  12 

12  29 

11 

14 

19 

7 

44 

13 

22 

Jan.  29. 

Total,  column 

I 

w . 

Average,  col- 

1 

iimn  (b) . 

[33 

14 

23 

19 

12 

17 

20 

14 

21 

30 

14 

19 

69 

14 

24 

27 

11 

15 

29 

13 

17 

7 

11 

12 

17 

12 

15 

10  12 

18  .. 

4 

16 

24 

3 

12 

14 

338 

12 

24 

Greatest,  col- 

umn  (c) . 

1 

1 

INVERSIONS  OF  15°  OR  MORE. 


1  Values  interpolated. 

(a)  Number  of  nights  during  which  inversions  of  5°,  10°,  15°,  and  20°  or  more  occurred  between  any  two  stations  of  slope. 

(b)  Average  (degrees)  of  inversion. 

(c)  Amount  in  degrees  of  greatest  inversion. 

(d)  Greatest  inversion,  date  of. 


THERMAL  belts  ANI)  FRUIT  GROWING  IN  NORTH  CAROLINA. 

Table  1C,.- Total  monthly  and  annual  number  of  inversions  of  5°,  10°,  15°,  and  20°  on  six  short  slopes,  1914. 

INVERSIONS  OF  5°  OR  MORE. 


63 


Stations. 


Blantyre . 

Blowing  Rock . 

Bryson . 

Hendersonville. . . . 

Highlands . 

Mount  Airy . 


Total,  column 

(a) . 

Average,  col¬ 
umn  (b) . 

Greatest,  col¬ 
umn  (c) . 


Jan. 

Feb. 

Mar. 

a 

b 

c 

d 

a 

b 

C 

d 

a 

b 

c 

d 

— 

‘ - 

— 

— 

— 

— 

16 

11 

18 

29 

12 

14 

15 

2 

12 

11 

20 

16 

8 

7 

11 

23 

3 

8 

10  27 

4 

6 

7 

16 

>16 

>7 

.. 

9 

8 

10 

2 

8 

8 

10 

16 

14 

10 

15 

29 

8 

11 

13,  2 

11 

916 

16 

9 

12 

17 

14 

7 

10 

12 

27 

7 

11 

21 

16 

7 

9 

13 

29 

6 

8 

10 

3 

7 

7 

10 

16 

70 

10 

18 

•• 

45 

10 

15 

-- 

49 

9 

21 

Apr. 


May. 


151015  23 
5j  91218 
17!  8  11;23 
1311  18  28 
13  13  22  22 
6  812  22 


69,10  22  . 


c  d 

11 16  23 
10  18  27 
8)  12  26 
1218  23 
15  25  22 
16  913  28 


June. 


a  ib 


120 


1125.. 


78 


19  . 


July. 


abed 


83 


7  [12 13 
812  23 
5  5  8 
81126 
10  22  24 
1012 


Aug.  I  Sept. 


ab  c  d  j  a  b  c  d 


"" 


22. 


49  8 


6  1914 
15  20  14 
5  24  1 
619 12 
15  18  18 
91911 


15 


70 


817 


Oct. 


abed 


7  11 
27  10 
6 

6  13 
5  16 
27  11 


66 


816  1 
8  14  22 
6  10  31 
812  31 


Nov. 


a  b  c 


1017 

610 


817 


114 


13  18 
915 

1017 
11  18 

14  25 
917 


11,25 


Dec. 


a  i  b  c  d 


10 
2 

4 

5  8,12  17 

141  1015  12 

4;  9111  24 


713  17 
9  12  28 
6!  7,  18 


39  8 


15  ... 


Annual. 


a  b  c 


168 

116 

109 

153 

191 

115 


852 


9  20 
818 
7  17 
918 
11  25 
817 


9  25 


Mar.  16. 
.May  27. 
Nov.  28. 
May  23. 
May  22. 
Nov.  3. 


INVERSIONS  OF  10°  OR  MORE. 


Blantyre . 

8 

14 

IS 

29 

6 

1245 

2 

7 

14 

20 

16 

9 

12 

15  23 

19 

13 

16 

23  2 

Blowing  Rock . 

1 

11 

11 

23 

1 

10  1C 

27 

3 

11 

Bryson . 

1 

1040 

? 

2 

10 

10 

£{  •• 

Hendersonville . 

8 

13 

15 

29 

7 

11 

13 

2 

4 

12 

16 

16 

9 

13 

18 

28 

19 

13 

18 

23  2 

Highlands . 

6 

13 

17 

14 

4 

11 

12 

27 

4 

15 

21 

16 

9 

15 

22 

22 

18 

15 

25 

22  12 

Mount  Airy . 

2 

12 

13 

29 

1 

10 

10 

3 

2 

10 

10 

16 

1 

12 

12 

22 

7 

n 

13 

28 

. 

Total,  column 

. 

Average,  col¬ 
umn  (b) . 

25 

13 

18 

.. 

20 

11 

15 

19 

12 

21 

36 

12 

22 

75 

13 

25 

16 

Greatest,  col- 

umn  (c; . 

12 


11 


19 


24  4 
3 


29  4 

30  9 
1 


21 


12 


22 


2 

12 

13 

7 

! 

313 

4!2 

1110 

341 

3 

12 

15 

20 

i 

a 

n 

27 

2 

10 

11 

6 

10 

12 

15 

18 

12 

12 

17 

5 

9 

13 

13 

12 

15 

-- 

17 

11 

17 

20 

12 

17 


19  14 
6  13 
11,  11 
13  14 
161  17 
1  17 


66 


14 


I 

17, 

14 
28  . 

7,  1 


2  12 
1  12 


12 
8j  12 


25  . 


10 


12 


13  17 
12  28 


15  ... 


81 

32 

23 

72 

115 

15 


338 


1218  Nov.  17. 
1218  May  27. 
10 17  Nov.  28. 
1118  Nov.  7. 
14j25  Nov.  7. 
12  17  Nov.  3. 


12  25 


INVERSIONS  OF  15°  OR  MORE. 


Blantyre . 

2 

17 

18 

29 

1 

15 

15 

2 

2 

18 

20 

16 

2 

15 

15 

23 

6 

15 

16 

23 

f 

1  Ifi 

16 

1 

8 

16 

15 

17 

10 

IS 

15 

17 

18 

7 

22 

16 

16 

17 

16 

17 

17 

20 

18 

17 

18 
25 
17 

Mar.  16. 

May  27. 

Nov.  28. 

May  23. 

Nov.  7. 

Nov.  3. 

Blowing  Rock . 

.. 

2 

17 

18 

27 

1 

15 

15 

20 

14 

28 

7 

Bryson . 

1 

1 

14 

Hendersonville . 

2 

15 

15 

29 

1 

16 

16 

16 

3 

16 

18 

28 

3 

17 

18 

23 

Highlands . 

3 

16 

17 

14 

1 

21 

21 

16 

6 

17 

22 

22 

9 

19 

25 

22 

6 

16 

19 

30 

.. 

6 

18 

22 

24 

15 

1 

17 

17 

16 

9 

1 

i 

15 

Mount  Airy . 

17 

17 

3 

1 

9 

Total,  column 

(a) . 

Average,  col¬ 
umn  (b) . 

7 

16 

18 

1 

15 

15 

4 

18 

20 

11 

16 

22 

20 

17 

25 

6 

16 

19 

6 

18 

22 

3 

15 

15 

1 

17 

17 

3 

16 

17 

25 

102 

25 

l 

15 

15 

88 

16 

25 

Greatest,  col¬ 
umn  (c.) . 

INVERSIONS  OF  20°  OR  MORE. 


(a)  Number  of  nights  during  which  inversions  of  5°,  10°,  15°,  and  20°  or  more  occurred  between  any  two  stations  on  slope. 

(b)  Average  (degrees)  of  inversion. 

(c)  Amount  (degrees)  of  greatest  inversion. 

(d)  Date  of  greatest  inversion. 


The  table  shows  that  November,  May,  and  April  have 
the  greatest  number  of  inversions  of  the  larger  amounts 
in  the  order  named,  especially  those  of  15°  or  more. 
The  colder  months  of  January,  February,  and  March 
are  also  well  represented  in  the  portions  of  the  table 
showing  the  larger  inversions;  August  has  practically 
no  large  inversions,  and  Ellijay,  Gorge,  and  Globe  are 
the  only  slopes  in  that  month  having  amounts  equaling 
10°,  no  slope  having  inversions  then  of  15°  or  more. 

In  the  discussion  of  Table  2a  under  the  subject  of 
“Average  minimum  temperature”  we  found  many 
cases  of  pronounced  inversions  during  the  selected 
clear  periods  of  May,  1913,  and  November,  1916,  and 
that,  as  a  rule,  the  largest  inversions  occurred  in  the 
May  period;  but  in  Table  13,  containing  the  number  of 
instances  of  inversions  of  5°  or  more  on  the  six  longest 
slopes,  we  find  that,  during  the  four-year  period  from 


1913  to  1916  not  only  do  the  greatest  number  of  inversions 
occur  in  November,  but  also  the  greatest  range  of  in¬ 
version.  However,  in  two  out  of  the  four  years,  1914 
and  1916,  the  number  of  inversions  in  May  exceeds 
those  in  November,  while  in  every  year  of  the  four  the 
average  degree  of  inversion  in  November  either  equals 
or  exceeds  the  average  in  May.  During  a  long  period 
of  years  there  would  doubtless  be  very  little  difference 
in  the  frequency  or  the  range  between  the  two  months. 

Inversions  of  stated  amounts  on  six  selected  short  slopes 
in  the  year  1914 ■ — Table  16  supplements  Table  14,  just 
as  Table  15  supplements  Table  13,  and,  moreover,  in 
presenting  data  for  varying  amounts  of  inversion  on 
six  short  slopes,  serves  as  a  comparison  with  Table  15. 

Table  16  contains  the  data  for  1914  for  Blantyre, 
the  Flat  Top  orchard  at  Blowing  Rock,  Bryson,  Hen¬ 
dersonville,  the  Waldheim  orchard  at  Highlands,  and 


64 


SUPPLEMENT  NO.  19. 


Mount  Airy,  ranging  in  vertical  height,  base  to  summit, 
from  350  feet  at  Blowing  Hock  to  750  feet  at  Henderson¬ 
ville.  The  figures  for  these  shorter  slopes  in  Tables  14 
and  16  generally  represent  inversions  between  the  base 
and  summit  stations,  wrhile  the  figures  for  the  long  slopes 
shown  in  the  other  tables  usually  represent  inversions 
between  the  base  and  certain  slope  stations  at  Altapass, 
Ellijay,  and  Tryon  and  between  the  base  and  summit 
stations  at  Cane  River,  Globe,  and  Gorge. 

On  the  short  slopes  under  discussion,  for  the  year  1914 
the  Waldheim  orchard  at  Highlands  stands  out  pre¬ 
eminently  as  having  the  largest  number  of  inversions 
of  stated  amounts,  5°,  10°,  15°,  and  20°,  and  this  record 
confirms  previous  statements  made  regarding  that  slope. 
While  the  total  number  of  inversions  of  5°  for  the  year 
1914  does  not  quite  equal  the  number  noted  in  the  same 
year  at  Ellijay,  196,  as  shown  in  Table  15,  the  frequency 
of  the  larger  inversions  is  always  greater  at  Highlands 
because  of  the  abnormally  low  minima  at  the  base 
station,  totaling  115  with  10°  or  more,  46  with  15°  or 
more,  and  13  with  20°  or  more.  During  inversions 
there  are,  in  fact,  often  extraordinary  differences  between 
the  temperature  at  the  base  station  and  No.  4,  200  feet 
above,  and  at  times  even  greater  differences  between  the 
base  and  the  summit  station,  No.  5. 

Blantyre  is  the  only  other  short  slope  which  has  an 
inversion  of  20°  or  more,  ranking  next  to  Highlands  in 
this  respect,  as  well  as  in  the  number  of  inversions  of 
5°,  10°,  and  15°.  Reference  has  been  made  frequently 
to  the  character  of  the  exposure  of  the  base  station  at 
Blantyre,  the  French  Broad  River  valley  at  that  point 
being  a  vast  frost  pocket,  and  it  is  because  of  the  low 
minima  at  No.  1  that  the  inversions  there  are  compara¬ 
tively  large  and  frequent.  Generally  speaking,  so  far  as 
large  inversions  of  15°  or  20°  are  concerned,  if  Highlands 
were  excepted  the  number  would  be  considerably  less  on 
the  short  slopes  than  on  the  long  ones. 

Taking  the  six  short  slopes  as  a  whole,  May  leads  in 
the  number  of  inversions  of  5°  and  10°  or  more,  with 
November  second,  while  November  leads  in  the  number 
of  15°  or  more  and  20°  or  more.  On  the  long  slopes 
(Table  15)  May  leads  only  in  the  smaller  inversions  of 
5°  or  more,  the  month  of  November  leading  with  the 
larger  inversions. 

Highlands  has  the  largest  number  of  the  smaller 
inversions  in  the  month  of  July,  25,  November  following 
with  22,  June  with  21,  and  May  with  20;  in  the  larger 
inversions  of  10°,  15°,  and  20°,  November  and  May 
easily  lead.  It  is  intersting  to  note  that  the  Waldheim 
orchard  at  Highlands  has  the  greatest  elevation  above 
sea  level,  not  only  of  the  six  slopes  included  in  Tables 
14  and  16,  but  also  of  all  the  slopes  in  the  entire  research. 

Effects  of  variation  in  vapor  pressure,  relative  humid¬ 
ity,  and  temperature,  upon  degree  of  inversion. — It  has 
been  shown  in  previous  chapters  that  the  frequency 
of  and  range  in  inversion  is  greatest  during  the  spring 
and  autumn  months,  mainly  because  in  those  periods 
of  the  year  in  the  Carolina  mountains  clear  weather 
predominates  to  a  much  greater  degree  than  in  other 
seasons,  areas  of  high  pressure  often  remaining  for  long 
periods.  However,  the  range  of  inversion  is  also  depen¬ 
dent  upon  other  causes — namely,  vapor  pressure,  rela¬ 
tive  humidity,  temperature,  wind  direction  and  velocity, 
and  soil  coveij 

Satisfactory  data  for  vapor  pressure  and  relative 
humidity  covering  the  period  of  the  research  for  the 
various  orchard  stations  are  not  available,  and  in  making 
a  comparison  between  degree  of  inversion  and  atmos- 
spheric  moisture  it  has  become  necessary  to  use  the 


humidity  observations  at  the  regular  station  of  the 
Weather  Bureau  at  Asheville,  located  in  the  heart  of 
the  mountain  region.  These  figures  cannot  be  expected 
to  give  the  exact  data  for  the  various  sections;  never¬ 
theless,  they  may  be  considered  to  be  approximately 
correct  for  the  stations  in  the  immediate  vicinity  having 
the  same  elevation  above  sea  level,  as  Hendersonville, 
Blantyre,  and  Cane  River. 

Figure  53  presents  in  graphic  form  the  variation  in 
relative  humdity  and  vapor  pressure  at  nightfall  for  the 
Asheville  Weather  Bureau  station  and  the  average 
range  of  inversion  the  following  morning  on  the  slopes 
at  Asheville,  Hendersonville,  Blantyre,  and  Cane  River 
in  certain  selected  clear  periods  of  inversion  weather  for 
the  12  months  of  the  year,  including  the  selected  May 
and  November  periods  appearing  in  Table  2a.  It  is 
apparent  that  there  is  a  striking  inverse  relation  between 
the  relative  humidity  and  average  range  of  inversion, 
the  maximum  degree  of  inversion  being  noted  in  May 


JAN  F£B  MAR  APR  MAY  JUN  JUL  AUG  SEP  OCT  NOV  DEC 


Fig.  53. — Relation  of  degree  of  inversion  to  variation  in  vapor  pressure  and  relative 
humidity.  R.  H.  =  rel.  humidity;  V.  P=vapor  pressure;  INV. —inversion. 


and  a  secondary  maximum  in  November  at  the  times 
of  the  two  minima  in  relative  humidity.  The  lines  in 
Figure  53  show  that  this  inverse  relation  is  constant, 
with  the  exception  of  a  slight  variation  in  the  month  of 
March. 

There  is  also  apparent,  generally  speaking,  an  inverse 
relation  between  the  range  of  inversion  and  the  vapor 
pressure,  although  the  relation  is  not  so  close  as  between 
the  relative  humidity  and  degree  of  inversion.  Vapor 
pressure  is  least  during  the  winter  months,  but  the  degree 
of  inversion  is  not  greatest  at  that  time,  because  of  the 
fact  that  the  air  is  so  often  disturbed  by  passing  storm 
areas  that  it  rarely  becomes  sufficiently  warmed  to 
ermit  convectional  exchanges  of  any  marked  extent 
etween  the  free  air  over  the  valley  and  the  surface  air 
on  the  slope  and  the  maximum  degree  of  inversion  is 
found  in  the  spring  and  autumn  months,  when  long 
periods  of  fair  weather  are  prevalent. 

The  range  of  inversion  is  the  least  during  the  summer 
months,  and  especially  during  August,  when  both  the 
relative  humidity  and  the  vapor  pressure  are  at  their 
maximum. 


65 


THERMAL  BELTS  AND  FRUIT  ( 

The  table  below  presents  additional  data  showing  the 
relation  between  the  vapor  pressure  and  the  ranm  of 
inversion  at  certain  selected  stations: 


Low  vapor  pressure. 
May,  1913 — 8  p.  m. 

High  vapor  pressure, 
June,  1914—8  p.  m. 

3 

4 

5 

20 

21 

22 

Vapor  pressure  (inches) . 

0.154 

9 

15 

11 

17 

0.193 

13 

24 

17 

21 

0.620 

0.708 

0. 664 

Inversions  (F°): 

Asheville . . 

Hendersonville . 

5 

6 

10 

5 

Blantvre . 

5 

Cane  River . 

8 

5 

8 

6 

- - — _ 

S 

During  the  first  period  selected,  May  3,  4,  and  5,  1913, 
the  weather  was  clear  and  the  wind  light,  with  small 
vapor  pressure,  and  the  degrees  of  inversion  were  large 
on  the  various  slopes.  In  the  second  selected  period, 
June  20,  21,  and  22,  1914,  the  weather  conditions  were 
much  the  same,  except  that  the  vapor  pressure  was 
much  greater,  with  small  inversions  in  consequence. 
During  the  dry  period  the  inversions  ranged  from  9°  to 
24°  and  during  the  humid  period  from  3°  to  10°. 

Table  17  brings  out  the  variation  in  inversion  on  a 
single  slope,  Ellijay,  during  humid  and  relatively  dry 
periods,  respectively.  These  humid  and  dry  periods 
consist  of  seven  days  each,  selected  as  typical,  the  vapor 


JROWING  IN  NORTH  CAROLINA. 

pressure  at  the  Asheville  Weather  Bureau  station  being 
employed,  the  pressure  averaging  for  the  humid  period 
0.572  inches  and  for  the  dry  period  0.298  inches.  It  is 
difficult  to  secure  more  than  two  clear  nights  in  succession 
in  the  mountain  region  with  high  humidity,  and  therefore 
the  two  periods  are  made  up  of  seven  individual  nights 
each. 

The  humid  period  is  characterized  by  a  small  average 
diurnal  range  in  temperature,  24.8°,  and  a  correspond¬ 
ingly  small  inversion  at  night,  4°,  between  Nos.  1  and  4. 
The  average  diurnal  range  during  the  dry  period  is  40.2°, 
nearly  twice  as  great  as  that  during  the  humid  period, 
and  the  average  inversion  during  the  dry  period  is  18° — ■ 
over  four  times  that  during  the  humid  period. 

In  the  humid  period  the  belt  of  highest  temperature 
rises  more  slowly  than  during  the  dry  period,  as  shown 
by  the  figures  in  bold-faced  type,  because  of  increased 
absorption  of  the  heat  by  the  air,  never  reaching  a 
greater  height  than  station  No.  4,  while  during  the  dry 
period  the  belt  rises  much  more  rapidly,  appearing 
almost  immediately  at  a  high  elevation  following  the 
setting  of  the  sun,  and  with  decreasing  wind  velocity, 
or  at  least  air  movement  from  an  unfavorable  direction, 
the  belt  gradually  works  itself  up  to  the  summit,  an 
elevation  of  1,760  feet  above  the  valley  floor,  and  remains 
there  several  hours — in  this  particular  case,  from  5  a.  m. 
until  10  a.  m.,  after  the  latter  hour  the  point  of  highest 
temperature  shifting  to  No.  1  on  the  valley  floor. 


Table  17. — Average  hourly  temperatures  during  clear,  humid  weather  and  clear,  dry  weather,  selected  periods,  Ellijay. 

HUMID  PERIOD. 


P. 

M. 

A. 

M. 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

Noon. 

No.  5 . 

75.3 

77.7 

77.3 

77.0 

74.7 

71.2 

67.3 

65. 6 

64.7 

64.0 

63.7 

63.0 

62.7 

62.2 

61.7 

61.3 

60.8 

61.5 

63.5 

65.0 

67.3 

09.5 

72.0 

73.5 

No.  4 . 

76.5 

7S.7 

78.5 

78.2 

76.7 

73.0 

68.0 

67.2 

60.5 

65.  V 

65.2 

64.8 

63.8 

63.7 

63.5 

62.7 

62.5 

62.5 

64.0 

66.7 

68.  5 

70.5 

72.8 

74.5 

No.  3 . 

78.7 

80.7 

SO.  2 

79.7 

78.7 

74.2 

71.0 

68.3 

67.0 

65.8 

65.  7 

64.2 

63.8 

63.2 

62.3 

61.5 

61.5 

01.5 

64.3 

67.5 

70. 5 

72.0 

74.7 

76.3 

No.  2 . 

SI.  2 

82.8 

82.0 

82.0 

80.2 

76.5 

72.  0 

68.8 

65.8 

64.8 

63. 3 

02.5 

61.5 

61.0 

60.5 

60.2 

59.5 

59.8 

62.2 

66.7 

70.3 

73.3 

76.8 

78.5 

No.  1 . 

81.3 

83.3 

82.7 

82.5 

80.5 

75.8 

71.3 

66.8 

64.2 

62.8 

61.7 

60.7 

60.0 

59.  5 

59.2 

59.0 

58.5 

59.3 

62.0 

66.7 

70.8 

74.0 

78.0 

79.7 

DRY  PERIOD. 


No.  5 . 

59.6 

60.4 

61.4 

60.0 

52.4 

51.2 

50.2 

49.4 

49.0 

48.2 

48.2 

47.8 

47.2 

46.6 

47.0 

47.2 

46.8 

46.8 

49.0 

51.2 

53.8 

57.6 

57.0 

59.6 

61.6 

59. 6 

57.4 

54. 6 

52.6 

51.6 

51.0 

50.4 

49.8 

49.0 

48.8 

48.2 

48.2 

47.6 

47.2 

46.8 

46.0 

46.8 

48.4 

50.  8 

53.4 

No.  3. . 

61.4 

64.0 

65. 4 

64.4 

00.2 

56.2 

52.0 

49.4 

48.0 

46.  S 

45.8 

44.6 

43.4 

43.4 

41.8 

41.8 

40.8 

39.8 

39.4 

40.0 

41.8 

47.8 

55.0 

No.  2 . 

61.6 

64.4 

65.8 

66.4 

61.8 

55.8 

50.0 

45. 6 

43.6 

42.2 

41.2 

40.2 

39.2 

38.4 

37.2 

37. 0 

36.6 

36.0 

35. 4 

35.  4 

37.2 

43.6 

54.6 

No.  1 . 

65.6 

67.6 

68.6 

61.4 

56.6 

48.6 

42.8 

39.8 

37.8 

36.6 

35.2 

34.2 

32.6 

32.0 

31.0 

30.2 

29.6 

29.0 

28.4 

30.4 

38.0 

48.8 

57.8 

Note. — Bold-faced  figures  indicate  position  of  highest  temperature  on  slope  at  each  hour. 


As  stated  previously  the  greatest  inversions  invariably 
occur  after  a  period  of  clear  anticyclonic  weather  and 
when  a  high  passes  to  the  east  or  south  of  the  region. 
Under  the  influence  of  sunshiny  days  the  temperature 
of  the  free  air  at  nightfall  acquires  an  initial  temperature 
higher  and  higher  on  each  succeeding  night,  thus  pro¬ 
ducing  larger  and  larger  inversions,  despite  the  fact  that 
the  atmosphere  naturally  becomes  slightly  more  humid 
as  the  period  advances.  However,  the  increase  in  tem¬ 
perature  is  usually  so  rapid  in  proportion  to  any  increase 
in  the  absolute  humidity  that  the  loss  through  radiation 
is  apparently  not  materially  affected,  hut  the  degree  of 
inversion  actually  increases  until  the  high  pressure  over 
the  region  gives  way  to  a  low  approaching  from  the 
west,  with  increasing  cloudiness,  when  the  inversions 
either  become  variable  or  diminish  in  degree,  depending 
upon  the  rapidity  of  the  eastward  movement  of  t  ie  low. 
Again,  during  the  closing  days  of  such  period  the  tem¬ 
perature  increases  slightly  as  compared  with  the  increase 
in  absolute  humidity,  and  this  condition  results  in  a 
decrease  in  the  loss  through  radiation  and  a  reduction 


in  the  amount  of  inversion.  On  this  account  the  last 
nights  of  a  clear  dry  period  do  not  show  the  degree  of 
inversion  that  may  be  apparent  during  the  middle  of  the 
period,  when  the  change  to  higher  temperature  is  rapid 
and  the  increase  in  water  vapor  slow. 

The  vapor  pressure,  then,  plays  a  most  important 
part  in  regulating  the  extent  of  inversions.  With  rela¬ 
tively  high  pressure  and  clear  weather  a  small  amount 
of  moisture  in  the  air  at  sundown  remaining  unchanged, 
or  even  increasing  slightly,  during  the  greater  portion  of 
the  night,  permits  free  radiation  and  loss  of  heat,  as  the 
drier  tne  air  the  greater  the  radiation  through  it.  On  the 
other  hand,  a  large  amount  of  water  vapor  in  the  atmos¬ 
phere  prevents  free  radiation,  as  the  heat  radiated  is 
largely  absorbed  by  the  vapor  and  does  not  pass  freely 
through  the  air.  As  an  inversion  is  distinctly  a  radiation 
phenomenon,  it  is  easily  seen  that  the  more  rapid  the 
radiation  the  greater  the  degree  of  inversion. 

As  the  degree  of  moisture  in  the  air  is  shown  by  the 
temperature  and  the  relative  humidity,  these  two 
factors  have  to  be  considered  in  determining  the  effect 


66 


SUPPLEMENT  NO.  19. 


of  absolute  humidity;  on  inversions.  Aside  from  other 
considerations,  the  higher  the  temperature  and  relative 
humidity  the  higher  the  absolute  humidity  and  the 
smaller  the  inversion,  the  lower  the  temperature  and  the 
lower  the  relative  humidity  the  lower  the  absolute 
humidity  and  the  greater  the  inversion,  while  between 
these  two  extremes  may  occur  combinations  of  high 
temperature  and  low  relative  humidity,  and  low  tempera¬ 
ture  and  high  relative  humidity,  the  absolute  humidity 
being  usually  relatively  higher  with  the  first  combina¬ 
tion  than  with  the  second.  As  both  low  temperature 
and  low  relative  humidity  never  occur  at  the  same  time 
in  the  Carolina  mountain  region,  except  in  the  winter 
when  other  important  factors  are  at  work  in  producing 
large  inversions,  it  is  only  in  May  with  increasing  tem¬ 
perature,  and  in  November  with  decreasing  tempera¬ 
ture,  that  we  find  the  most  favorable  conditions  that 
cause  inversions,  considering  humidity  and  temperature 
alone.  Moreover,  in  these  two  months  the  other  factors 
which  aid  in  producing  inversions — high  pressure  and 
clear  quiet  weather — are  usually  present  in  greatest 
force.  Hence  inversions  have  both  their  greatest  fre¬ 
quency  and  range  in  May  and  November,  depending 
upon  which  month  the  most  favorable  combinations 
occur.  However,  it  is  probable  that  of  May  and  Novem¬ 
ber  the  largest  inversions  usually  occur  in  the  latter, 
aside  from  other  considerations,  simply  because  of  the 
greater  length  of  night  in  which  radiation  and  conse¬ 
quent  building  up  of  inversions  may  take  place. 

To  sum  up,  nights  in  which  the  temperature  is  moderate 
or  above  normal,  those  occuring  in  spring  and  autumn, 
for  instance,  with  low  relative  humidity  and  low  absolute 
humidity,  have  the  largest  inversions,  while  those  having 
relatively  high  temperature  with  high  relative  humidity 
and  high  absolute  humidity  produce  little  or  no  inversion; 
and  between  these  two  extremes  may  occur  varying 
amounts  of  inversion,  depending  upon  which  factor  or 
factors  exert  a  predominating  influence. 

Blair  5  has  found  that  in  early  winter  with  abnormally 
low  surface  temperatures  the  vertical  gradients  of  both 
temperature  and  vapor  pressure  are  small  as  compared 
with  those  in  early  spring  and  summer  and  that,  in 
consequence,  radiation  is  less  effective  in  early  winter. 
This  may  be  an  additional  reason  why  inversions  are  not 
larger  on  clear  calm  nights  in  winter. 

Hann  0  states  that  in  the  Alps  November  and  December 
and  the  first  half  of  January  are  the  most  favorable  for  the 
occurrence  of  inversions,  because  the  nights  are  then  the 
longest,  but  he  probably  has  in  mind  the  extreme  range 
of  individual  inversions  rather  than  the  average  range 
and  the  frequency,  so  far  as  the  winter  season  is  con¬ 
cerned.  While  large  individual  inversions  are  noted  in 
that  season  in  the  Carolina  mountain  region,  they  are 
not  as  large  nor  is  the  average  as  large  as  in  the  spring 
and  autumn,  and  especially  in  May  and  November. 

Effect  of  wind  direction  and  velocity  upon  degree  of 
inversion. — The  effect  of  wind  direction  and  velocity 
upon  inversion  is  also  sometimes  considerable.  It  has 
already  been  stated  that  inversions  are  of  little  con¬ 
sequence  unless  there  is  a  calm  or  the  wind  is  light  in  the 
lower  levels,  but  moderate  and  even  fresh  winds  often 
serve  to  increase  the  degree  of  inversion  in  the  upper 
levels  during  the  Intermediate  or  Cyclonic  Type  of  in¬ 
version.  Moreover,  when  the  topographical  conditions 
are  such  as  to  produce  a  mountain  breeze  down  the  slope 

1  Blair,  Wm.  R.,  Summary  of  the  free  air  data  obtained  at  Mount  Weather.  Bulletin, 
Mount  Weather  Observatory,  1913,  vol.  6. 

« Handbook  of  Climatology,  by  Julius  Hann,  p.  259.  English  translation  by  Ward. 


into  the  valley  the  temperature  rises  upon  the  floor,  and 
the  degree  of  inversion  is  lessened  in  consequence. 

Again,  the  wind  direction  is  a  factor  bearing  upon  the 
degree  of  inversion,  even  though  the  breeze  be  light. 
When  at  night  the  wind  blows  toward  the  slope,  it  brings 
an  increasing  supply  of  warm  free  air  to  the  upper  levels, 
increasing  the  degree  of  inversion,  in  contrast  with  the 
condition  when  the  wind  blows  away  from  the  slope. 

Table  18  presents  inversion  data  for  the  five  slopes  at 
Altapass,  Blantyre,  Blowing  Rock,  Tryon,  and  Wilkes- 
boro  for  two  selected  nights,  December  5,  1913,  and 
November  4,  1916,  the  fox-mer  with  moderate  northerly 
and  the  latter  with  light  southerly  winds.  The  direction 
of  the  slope  is  shown  in  connection  with  the  numbers 
of  the  stations. 

On  every  one  of  these  slopes  the  inversion  is  greater 
when  the  prevailing  wind  is  blowing  toward  the  slope. 
The  same  dates  have  been  selected  for  all  the  places, 
and  although  on  December  5  inversions  occurred  at 
Blantyre  and  Wilkesboro  the  influence  of  the  northerly 
winds  was  sufficient  on  the  southeast  slopes  at  Altapass, 
Blowing  Rock,  and  Tryon  to  produce  norms  instead, 
where  the  lowest  temperatures  were  registered  at  the 
most  elevated  points.  On  that  same  night  an  inversion 
of  11°  occurred  at  No.  2,  Wilkesboro,  on  a  northerly 
slope  150  feet  above  the  base,  while  Nos.  3  and  4,  located 
on  small  knobs  with  relatively  free  exposures  to  all 
winds,  were  affected  but  slightly.  At  Blantyre  No.  2, 
with  a  northwest  exposure,  there  was  an  inversion  of  10°, 
while  at  the  highest  station,  No.  4,  located  near  the 
summit  of  the  slope,  the  wind  direction  is  not  an  im¬ 
portant  factor,  just  as  at  Nos.  3  and  4  at  Wilkesboro. 

The  inversions  on  the  night  of  November  4,  1916, 
with  southerly  winds  were  quite  pronounced  on  the 
southeast  slopes  at  Altapass,  Blowing  Rock,  and  Tryon, 
in  contrast  with  the  night  of  December  5,  1913.  At  the 
highest  level  at  Wilkesboro,  No.  4,  on  the  November 
date  the  great  inversion  noted  in  Table  18  is  not  due  so 
much  to  the  effect  of  the  wind  in  causing  a  high  reading, 
there  as  to  its  effect  in  allowing  uninterrupted  loss  of 
heat  through  radiation  at  No.  1. 

The  wind  direction  plays  an  unusual  part  in  the  degree 
of  inversion,  as  will  be  further  shown  in  discussing  in¬ 
version  conditions  on  individual  slopes.  The  direction 
and  velocity  have  an  important  bearing  upon  the  de¬ 
velopment  of  the  mountain  breeze  down  the  slope  where 
the  surface  area  above  is  great  and  the  wind  is  calm,  or 
at  least  not  blowing  from  an  unfavorable  direction. 
The  breeze  often  develops  on  a  night  of  inversion,  de¬ 
scending  the  slope  and  raising  the  temperature  on  the 
valley  floor,  and  thus  preventing  injury  to  vegetation. 
However,  unless  the  surface  area  above  is  great  this  breeze 
does  not  develop.  Instances  of  the  effect  of  the  mountain 
breeze  on  the  valley  floor  at  Blowing  Rock  and  Tryon 
will  be  later  shown  by  the  thermograph  traces;  also  the 
effect  of  variation  in  wind  locally  at  Hendersonville  and 
Mount  Airy. 

Inversions  seldom  occur  when  strong  winds  prevail 
from  a  northerly  or  westerly  quarter,  or  when  the  temper¬ 
ature  is  falling  generally  along  the  entire  slope,  because 
then  norm  conditions  prevail,  and  this  is  also  the  case 
when  the  weather  is  cloudy. 

Table  18  contains  the  minimum  temperatures  on  two 
selected  nights  of  inversions,  one  with  northerly  and  the 
other  with  southerly  winds,  together  with  the  differences 
between  the  base  station  and  those  higher  up  on  the 
respective  slopes;  also  the  difference  in  elevation  between 
station  No.  1  and  those  above. 


THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 


Table  18.  Effect  of  wind  direction  and  velocity  on  inversions . 


Principal  and  slope  stations;  elevation 
of  base  station  (feet). 


Altapass: 

No.  1  (base),  elevation,  2,230. 

No.  2  (SE.) . . 

No.  3  (SE.) . 

No.  4  (SE.) . 

No.  5  (summit) . 

Blantyre: 

No.  1  (base),  elevation,  2,090. 

No.  2  (NW.) . . 

No.  3  (NW.) . 

No.  4  (NW.) . 

Blowing  Rock: 

No.  1  (base),  elevation  3,130. 

No.  2?s.) . ;.... 

No.  3  (base),  olevation  3,580. 

No.  4(SE.) . 

No.  5(SE.) . 

Try  on: 

No.  1  (base),  elevation  950... 

No.  2  (SE.) . 

No.  3  (SE.) . ; . 

No.  4  (SE.) . 

Wilkesboro: 

No.  1  (base),  elevation  1,240. 

No.  2  (N.) . 

No.  3(N.) . 

No.  4(W.) . 


Height 
of  slope 
station 
above 
base 
(feet). 

Northerly 
winds,  Deo.  5, 
1913. 

Southerly 
winds,  Nov.  4, 
1916. 

Min. 

Dif. 

Min. 

Dif. 

43 

32 

250 

41 

-2 

40 

+8 

500 

40 

-3 

39 

+7 

750 

38 

-5 

35 

+3 

1,000 

37 

-6 

34 

+2 

26 

28 

300 

26 

0 

27 

-1 

450 

36 

+10 

33 

+5 

600 

34 

+8 

39 

+11 

39 

35 

450 

39 

0 

45 

+10 

39 

28 

625 

39 

0 

40 

+12 

800 

37 

-2 

39 

+11 

51 

39 

380 

49 

-2 

46 

+7 

570 

47 

-4 

47 

+  8 

1, 100 

42 

-9 

45 

+6 

36 

29 

150 

47 

+  11 

33 

+4 

350 

48 

+  12 

40 

+  11 

430 

48 

+12 

46 

+  17 

Effect  of  variation  of  soil  cover  upon  degree  of  inversion. — 
In  connection  with  the  various  seasons  density  of  vege¬ 
tation  also  is  effective  In  lowering  the  night  temperature 
and  increasing  the  degree  of  inversion.  Radiation  from 
vegetation  is  most  free,  almost  as  great  as  from  an  ideal 
black  body,  and  where  the  vegetation  is  dense  on  the  val¬ 
ley  floor  and  the  summit  practically  free  from  growth 
the  effect  is  considerable.  This  is  especially  noticeable 
during  the  period  of  growth.  While  the  maximum 
degree  of  vegetation  is  not  reached  in  the  Carolina 
mountain  region  during  May,  except  at  the  lower  levels, 
nevertheless  vegetation  has  apparently  some  effect  at 
that  time  upon  the  degree  of  inversion.  By  November 
the  vegetation  has  changed  considerably,  but  the  in¬ 
fluence  then  of  the  longer  nights  predominates.  In  the 
winter  season  there  is  usually  no  difference  in  the  vegetal 
cover  along  an  entire  slope  from  summit  to  base,  but  there 
is  likely  to  be  more  snow  in  the  higher  levels,  and  because 
of  great  loss  of  heat  through  radiation  from  a  snow- 
covered  surface  inversions  may  not  be  as  large  then  on 
that  account,  aside  from  other  considerations  already 
stated. 

Inversions  on  individual  slopes  as  affected  by  topog¬ 
raphy. — Having  now  brought  out  the  distinguishing 
features  of  inversions  as  affected  by  weather  conditions 
and  soil  covering,  it  seems  necessary  to  present  addi¬ 
tional  data  for  selected  individual  slopes.  Reference  will 
here  be  made  to  certain  tables  and  illustrations  in  order  to 
indicate  the  influence  of  topography  in  all  its  phases  on 
the  phenomenon  of  inversion.  In  this  discussion  of  in¬ 
dividual  groups  some  of  the  statements  made  in  preceding 
pages  will,  necessarily,  be  repeated  so  as  to  cover  fully  the 
various  situations;  but  this  can  hardly  be  avoided. 

Altapass  and  Ellijay. — Judging  from  the  figures  found 
in  Tables  2  and  2a,  containing  mimimum  temperature  and 
inversion  data,  one  would  conclude  that  inversions  of 
considerable  amount  seldom  occur  on  the  Altapass  slope, 
but  this  is  only  because  No.  1  is  not  a  proper  base  station 
for  comparison  with  those  higher  up,  as  it  is  located  far 
above  the  valley  floor.  In  order  to  establish  definitely 
the  fact  that  on  this  slope  inversions  do  occur  which  com- 

Sare  favorably  with  those  on  other  slopes,  a  place  called 
orth  Cove,  about  2  miles  down  the  slope  and  730  feet  in 
vertical  distance  below  No.  1,  may  be  designated  as  an 


imaginary  base  station  and,  for  convenience,  be  termed 
station  No.  la.  It  is  fairly  representative  of  valley-floor 
conditions  and  can  properly  be  considered  the  base  of  the 
Altapass  slope.  In  elevation  No.  la  is  about  1,730  feet 
below  No.  5,  located  on  the  ridge,  the  vertical  distance 
between  the  two  points  being  only  30  feet  less  than  that 
between  the  base  and  summit  stations  at  Ellijay,  the 
longest  slope  employed  in  the  research,  1,760  feet.”  The 
elevation  above  sea  level  of  No.la  in  North  Cove  is  1,500 
feet,  about  equal  to  that  of  the  base  station  at  Gorge,  only 
15  miles  distant,  the  average  minimum  temperatures  of 
which  during  inversion  periods  are  doubtless  approxi¬ 
mately  the  same  as  those  at  North  Cove. 

The  table  following  embraces  data  for  Altapass  and 
Ellijay  for  the  May  and  November  selected  periods  of  in- 
inversion  shown  in  Table  2a,  but,  in  addition,  No.  la 
appears  as  the  base  station  for  Altapass,  with  readings 
estimated  from  the  records  of  the  Gorge  base  station  and 
estimated  readings  for  the  May  period  for  station  No.  5  at 
Ellijay,  the  latter  not  having  been  in  operation  in  1913. 


Stations  and  description. 

May  1-6, 1913. 

Nov.  2-5, 1916. 

Aver¬ 

age. 

Differ¬ 

ence. 

Aver¬ 

age. 

Differ¬ 

ence. 

Altapass: 

No.  la  base  station  1,500  feet  above  sea  level _ 

No.  1,  southeast,  730  feet  above  base . 

42.0 

50.3 

+8.3 

31.2 
39.  8 

+8.6 

No.  2,  southeast,  980  feet  above  base . 

55.2 

+13.2 

42.5 

+11.3 

No.  3,  southeast,  1,230  feet  above  base . 

53.3 

+  11.3 

40.8 

+9.6 

No.  4,  southeast,  1,480  feet  above  base . 

51.3 

+  9.3 

39.5 

+8.3 

No.  5,  summit,  1,730  feet  above  base . 

49.7 

+7.7 

39.5 

+8.3 

Ellijay: 

No.  1,  base  station  2,240  feet  above  sea  level . 

No.  2,  north,  310  feet  above  base . 

41.5 

49.0 

+7.5 

30.0 

34.0 

+4.0 

No.  3,  north,  620  feet  above  base . 

53.3 

+11.8 

39.0 

+9.0 

No.  4,  north,  1,240  feet  above  base . 

58.5 

+  17.0 

46.5 

+16.5 

No.  5,  summit,  1,760  feet  above  base . 

58.0 

+16.5 

45.0 

+15.0 

Readings  at  No.  la  Altapass,  May  and  November  periods,  and  at  No.  5,  Ellijay,  May 
period,  estimated. 


With  the  use  of  these  figures  it  is  apparent  that  station 
No.  1  at  Altapass,  up  to  the  present  considered  as  the 
base  station,  averages  considerably  higher  than  No.  la 
during  periods  of  inversion.  In  May  the  excess  at  No.  1 
is  8.3°  and  in  November  8.6°.  The  center  of  the  thermal 
belt  is  shown  here  to  be  near  station  No.  2,  with  excesses 
in  both  periods  of  11°  to  13°.  From  No.  2  upward  to  the 
summit  the  temperature  gradually  decreases  during 
inversion  weather,  although  in  the  November  period  the 
summit  station,  1,730  feet  above  the  base,  has  as  high  an 
average  minimum  as  station  No.  4,  250  feet  below. 
While  station  No.  5  at  the  summit  averages  higher  than 
No.  la,  it  is  rarely  the  warmest  on  the  entire  slope  and 
only  on  especially  favorable  nights  and  at  individual 
hours,  rather  than  through  the  entire  night. 

The  middle  of  the  thermal  belt  at  Altapass  usually 
lies  between  Nos.  2  and  3,  whether  we  consider  No.  1  or 
No.  la  as  a  base,  the  latter  being  used  merely  to  show  that 
large  inversions  do  occur  on  this  slope. 

At  Ellijay,  as  shown  by  the  table,  there  is  an  increase 
in  temperature  more  or  less  regular  from  base  to  station 
No.  4,  1,240  feet  above  the  valley  floor,  and  this  point 
marks  the  usual  position  of  the  center  of  the  thermal 
belt  on  that  slope,  although  sometimes,  under  favorable 
conditions,  the  center  reaches  to  the  very  summit. 

Above  Altapass  No.  3  the  minimum  temperature  is 
usually  lower  during  nights  of  inversion,  both  because 
of  the  increase  in  elevation  and  because  of  the  increasing 
area  of  radiating  surface,  the  cool  air  overlying  the 
plateau  above  being  in  close  proximity.  The  summit 
area  along  the  main  ridge,  where  station  No.  5  is  located, 
is  unusually  great,  no  other  summit  station  having  similar 


68 


SUPPLEMENT  NO.  19. 


environment,  and  with  the  possible  exception  of  Try  on 
there  is  no  other  slope  so  affected  during  nights  of  inver¬ 
sion.  However,  comparative  figures  can  not  be  given  for 
Tryon,  as  the  highest  station  employed  there  during  the 
period  of  the  research  was  considerably  below  the  summit. 
Figures  26  and  21 — contour  maps  of  Altapass  and  Tryon, 
respectively— bring  out  this  situation  as  regards  summit 
area.  The  loss  of  heat  from  this  great  area  along  the 
ridge  is  rapid  in  the  clear  weather  usually  favorable  for 
inversions  and  almost  always  sufficient  to  prevent  the 
center  of  the  thermal  belt  from  reaching  the  summit, 
and  generally  its  influence  is  sufficient  to  keep  the  center 
of  the  belt  down  to  the  level  of  Nos.  2  and  3  at  Altapass, 
just  as  at  Tryon,  even  though  the  temperature  at  the 
summit  is  often  higher  than  at  the  base.  The  situation 
at  the  Ellijay  summit  is  much  like  that  on  the  isolated 
peaks  at  Cane  River  and  Gorge,  where  the  center  of  the 
thermal  belt  is  usually  close  to  the  summit.  It  is  only 
when  the  winds  are  southerly  that  the  center  of  the 
thermal  belt  at  Altapass  is  at  the  level  of  the  summit, 
as  then  the  warm  free  air  flows  on  to  the  slopes. 

JANUARY  3  1916  4  ALTAPASS  -P 


Fig.  54. — Thermograph  traces,  January  3-5,  1916,  stations  Nos.  1  and  5,  Altapass,  show¬ 
ing  importation  of  warm  air  at  summit. 


Fig.  55. — Thermograph  traces,  May  2-3,  1913,  north  and  south  facing  slopes,  Asheville- 


Figure  54  shows  a  norm  condition  at  Altapass  during 
most  of  the  night  of  January  3-4,  1916,  followed  by  a 
quick  recovery,  while  on  the  following  night,  the  5 th , 
under  the  influence  of  a  rapidly  approaching  low,  an 
inversion  of  the  Cyclonic  Type  occurred,  the  thermograph 
at  No.  5  beginning  to  rise  as  early  as  1  a.  m.,  while  that  at 
No.  1  fell  slightly.  At  7  a.  m.  on  the  5th  the  temperature 
at  No.  5,  the  summit,  was  the  highest  on  the  slope,  ex¬ 
ceeding  the  reading  at  that  hour  at  No.  1  by  13°.  Under 
the  discussion  of  inversions  at  Cane  River  other  similar 
marked  examples  of  rises  in  temperature  will  be  explained. 

Asheville. — It  has  been  shown  that  the  highest  min¬ 
ima  during  inversion  weather,  without  exception,  are 
found  at  the  most  elevated  stations  on  each  of  these  two 
facing  slopes,  No.  3  and  No.  3a,  and  that  the  stations  on 
the  south  slope  nearly  always  average  higher  than  those 
on  the  opposite  northerly  slope,  there  being  a  greater 
difference  in  minima  between  Nos.  2  and  2a  than  between 
Nos.  3  and  3a,  because  of  a  correspondingly  greater  dif¬ 


ference  in  inclination  of  slope  at  the  two  former  stations 
than  at  those  higher  up,  as  explained  under  the  discussion 
of  “Average  minimum  temperatures.”  Figure  55  shows 
the  differences  in  temperature  prevailing  between  Nos.  2 
and  2a  on  a  clear  quiet  night.  No.  2  is  located  on  a 
slight  grade  where  the  cold  air  sometimes  accumulates, 
while  No.  2a  is  situated  on  a  steep  slope  and  has  better 
opportunity  for  exchange  with  the  warm  free  air.  More¬ 
over,  the  southerly  slope  being  heated  more  during  days 
of  sunshine  than  the  northerly  slope  naturally  should 
have  somewhat  higher  ensuing  minima.  This  graph  also 
contains  examples  of  sudden  rises  in  night  temperature 
due  to  the  mechanical  heating  of  cold  air  brought  down 
from  the  slope  above,  as  described  in  detail  on  previous 
pages.  Asheville  No.  2  is  ideally  situated  to  show  such 
irregularities  in  temperature  on  clear  quiet  nights. 

Blantyre. — In  Figure  56  are  shown  thermograph  traces 
at  the  four  Blantyre  stations  during  a  typical  inversion 
period,  November  12-14,  1913.  The  peculiar  location 
of  No.  2,  so  far  as  radiation  is  concerned,  is  well  illustrated 
by  the  frequently  large  fluctuations  in  temperature  on 


each  of  the  two  nights  when  the  air  in  the  sag  at  No.  2, 
having  become  colder  than  that  lower  down,  moved  out 
and  down  the  slope,  at  the  same  time  being  replaced  by 
the  warm  free  air  adjoining.  Similar  fluctuations  in 
temperature  are  noted  on  slopes  at  Gorge  No.  3  and  Ashe¬ 
ville  No.  2.  Blantyre  No.  1,  of  course,  being  situated 
close  to  a  true  valley  floor,  with  no  marked  irregularities 
in  topography  in  its  vicinity,  experiences  on  such  nights 
a  steady  decline  in  temperature  under  continuous  and 
uninterrupted  radiation,  as  illustrated  in  Figure  56.  Al¬ 
though  the  grass  around  Blantyre  No.  1  has  been  kept 
rather  short,  the  bottom  lands  generally  are  covered  with 
a  dense  growth  of  vegetation,  which  favors  rapid  loss  of 
heat  on  clear  quiet  nights,  and  as  the  slope  of  the  valley 
is  very  slight  at  that  point  the  area  may  be  likened  to  a 
vast  frost  pocket  during  nights  of  inversion  with  especi¬ 
ally  low  minima. 

The  curves  of  temperature  at  the  two  stations  on  the 
slope,  Nos.  3  and  4,  shown  in  Figure  56,  resemble  each 
other  much  more  closely  than  those  at  the  two  lower 
stations.  Tiffs  graph  also  shows  the  largest  inversion 
at  any  hour  noted  at  Blantyre  during  the  research,  27°, 
between  Nos.  1  and  4  at  8  a.  m.  on  November  14.  On 
the  13th  a  difference  of  26°  was  recorded  between  the 


69 


THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 


summit  and  base  stations.  During  the  same  period 
unusually  large  inversions  were  observed  generally  over 
the  mountain  region,  that  at  Gorge,  31°  at  6  a.  m.  on 
the  13th,  being  the  greatest  at  any  location  during  the 
four  years  of  record.  This  graph  also  shows  the  ex¬ 
tremely  large  range  in  temperature  common  to  valley 
floor  stations  under  favorable  conditions,  in  this  par¬ 
ticular  instance  the  temperature  at  No.  1  rising  from  a 
minimum  of  21°  to  a  maximum  of  73°  on  the  13th. 

The  middle  of  the  thermal  belt  at  Blantyre  would 
almost  always  lie  considerably  above  the  level  of  the 
summit  of  Little  Fodderstack  were  the  slope  higher, 
judging  from  a  comparison  of  temperatures  with  No. 
3a  at  Asheville,  the  latter,  with  an  elevation  150  feet 
higher,  always  having  higher  minimum  readings. 

Blowing  Rock  and  Highlands. — The  effect  of  wind 
direction  and  velocity  is  well  shown  in  Figure  57,  which 
contains  copies  of  the  thermograph  sheets  at  stations 


winds,  but  as  soon  as  the  wind  velocity  decreases,  as 
shown  by  the  hours  of  10  p.  m.  and  midnight,  No.  3  fell 
below  the  readings  at  station  No.  5,  because  loss  of  heat 
through  radiation  was  then  allowed  to  continue  without 
being  offset  by/  turbulence.  With  a  slight  increase  in 
velocity  after  midnight,  note  the  rise  in  temperature  at 
No.  3,  and  with  a  further  decrease  to  calm  during  the 
hours  from  4  to  8  in  the  morning  of  the  2d,  note  the 
fall  at  No.  3.  The  night  of  the  2d-3d  shows  the  effect 
of  a  light  mountain  breeze  in  that  the  temperature 
at  No.  3  is  prevented  from  falling  to  a  low  point, 
partly  because  the  air  in  descending  the  slopes  of 
the  Flat  Top  orchard  is  slightly  warmed  by  compres¬ 
sion.  By  2  a.  m.  on  the  3d  the  temperature  at  No. 
3  is  higher  than  at  No.  5  and  continues  so  until  sunrise. 
Thus  a  condition  resembling  a  “top  freeze”  is  formed. 
Shortly  after  sunset  on  the  4th  the  wind  changed  to 
southerly,  increasing  at  first,  but  later  gradually  di- 


Blowing  Bock  Jdov  z  IQI6 


^  F  WiLl  °  °  °  \  LjGii  ^  h  \|\  hi  °*\f 


Wind  Direction  and  l/e/ocittf  from  Ashe  d t/e  Records  (  sards ‘M/t-ES  per  hour) 

Fig.  57. — Thermograph  traces,  November  1-5, 1916,  stations  Nos.  1,  2,  3,  and  5,  Blowing  Rock;  also  wind  direction  and  velocity  at  Asheville. 


Nos.  1,  3,  and  5  at  Blowing  Rock  for  the  period  from 
November  1  to  5,  1916,  together  with  hourly  wind 
directions  and  velocities  taken  from  the  records  of  the 
Weather  Bureau  office  at  Asheville  for  the  same  period. 
The  light  broken  line  is  a  trace constructedforcomparative 
purposes  from  daily  extremes  recorded  at  Banners  Elk, 
N.  C.,  at  practically  the  same  elevation,  but  a  few  miles 
distant  from  the  edge  of  the  plateau.  The  weather 
during  this  period  was  clear  and  dry.  In  the  upper 
portion  of  the  graph  a  comparison  is  shown  between 
Nos.  3  and  5,  located  in  the  Flat  Top  orchard,  and  it 
will  be  seen  how  quickly  the  temperature  changes, 
especially  during  the  night,  in  response  to  a  change  in 
direction  and  velocity  of  wind,  even  though  the  change 
in  the  latter  be  small.  The  lower  part  of  the  graph 
compares  No.  1,  located  in  the  China  orchard,  with  No. 
5,  in  the  Flat  Top  orchard. 

During  the  early  evening  of  the  1st  the  temperature 
in  the  Flat  Top  orchard  (upper  portion  of  graph)  is 
kept  fairly  uniform  by  the  light  to  moderate  northwest 


minishing  until  it  reached  a  calm  about  9  a.  m.  This 
light  southerly  wind  brought  large  amounts  of  warm 
free  air  to  the  slope  at  the  elevation  of  No.  5,  while  No. 
3  at  the  foot  of  the  slope  is  not  affected,  loss  of  heat 
continuing  there  unimpeded  during  the  night,,  except 
from  11  p.  m.  to  2  a.  m.,  when  the  wind  changed  to  east¬ 
erly  and  a  slight  rise  in  temperature  occurred.  With  a 
change  in  direction  again  to  south,  the  temperature  fell. 
This  night  of  the  3d-4th  is  an  excellent  example  of  large 
inversions  in  both  orchards,  as  shortly  after  10  p.  m. 
the  temperature  at  No.  4  was  about  16°  higher  than  No. 
3  for  a  difference  in  elevation  of  175  feet,  and  No.  2  in 
the  China  orchard  at  the  same  hour  was  about  10° 
higher  than  No.  1  for  a  difference  in  elevation  of  450  feet. 

*ldie  same  response  to  change  in  wind  direction  and 
velocity  can  be  followed  in  the  thermograph  traces  in  the 
lower  portion  of  the  graph,  only  the  effects  are  not  so 
marked  in  the  China  orchard  because  of  difference  m 
topography.  Thus  we  see  how  important  in  determining 
the  extent  of  inversion  at  Blowing  Rock  is  this  factor  of 


70 


SUPPLEMENT  NO.  19. 


wind,  and  the  effect  does  not  necessarily  appear  in  average 
conditions  or  even  in  the  daily  minimum  temperatures, 
because  during  portions  of  the  same  night  entirely  different 
conditions  may  prevail.  On  the  night  of  the  lst-2d,  the 
minimum  at  No.  3  was  about  33°  at  7 :30  a.  m.,  the  lowest 
reached  at  any  station  during  the  night,  yet  shortly 
after  midnight  the  temperature  at  No.  3  was  over  6° 
higher  than  at  No.  5,  which  at  that  time  was  the  lowest 
in  the  orchard. 

This  influence  of  the  mountain  breeze  at  Blowing 
Rock  No.  3  is  the  main  reason  why  the  temperature 
there  on  some  nights  is  so  much  higher  than  at  High¬ 
lands  No.  3  and  also  why  the  number  of  large  inversions 
in  the  Flat  Top  orchard,  at  the  base  of  which  No.  3  is 
located,  is  so  much  smaller  than  the  number  in  the 
Waldheim  orchard  at  Highlands  (see  Tables  14  and  16). 
Both  No.  3  stations  at  Highlands  and  Blowing  Rock 
have  about  the  same  elevation,  with  annual  mean 
temperatures  for  the  period  of  observations  differing  by 
only  0.3°  (see  Table  4).  The  surface  area  in  the  vicinity 
of  the  higher  levels  of  the  Blowing  Rock  orchard  station 
No.  5  is  considerable,  being  almost  flush  with  the  plateau 
on  which  the  air  is  rapidly  chilled  through  radiation  on 
clear  nights,  and  in  flowing  down  the  slopes  of  the  orchard 
it  finds  an  outlet  below  No.  3,  so  that  this  descending 
current,  being  warmed  mechanically,  often  prevents  the 
temperature  at  No.  3  from  falling  to  as  low  a  point  as  it 
otherwise  would.  In  the  China  orchard  this  descending 
air  doubtless  passes  over  No.  1  at  a  considerable  elevation 
and  ordinarily  does  not  affect  the  temperature  at  that 
station,  which  is  located  on  a  rather  steep  slope,  much 
unlike  No.  3  in  the  Flat  Top  orchard.  Highlands  No.  3 
has  no  such  mountain  breeze,  as  it  is  located  in  a  small 
saucer-shaped  depression  with  no  outlet  below  a  slope 
culminating  in  a  knob.  A  slope  on  one  side  and  timber 
on  the  other  sides  completely  surround  this  small  pocket. 

Cane  River. — The  slope  at  Cane  River  is  rather  steep 
and  culminates  in  two  isolated  peaks  or  knobs,  Avith  gen¬ 
erally  sharp  profile  and  small  mass  in  proportion  to  eleva¬ 
tion,  rising  considerably  above  the  surrounding  country 
within  a  radius  of  several  miles.  All  these  factors,  with 
their  resulting  reduction  of  radiating  surface  near  the 
summit  and  the  better  exposure  to  the  great  mass  of  free 
ah-  which  faces  the  higher  stations,  cause  the  temperature 
at  No.  4,  located  on  one  of  the  knobs,  to  approach  that  of 
the  free  air  on  nights  with  lights  winds. 

This  effect  of  the  free  air  temperature  at  No.  4  is  more 
marked  than  at  any  other  individual  station  in  the  re¬ 
search.  In  fact,  during  January,  1915,  it  Avas  so  marked 
as  to  sIioav  in  the  hourly  values  when  the  average  tempera¬ 
ture  at  No.  4  gradually  and  continuously  rose  after  mid¬ 
night,  the  minimum  occurring  the  previous  evening. 
These  rises  in  temperature  at  summit  stations  constitute 
one  of  the  most  interesting  features  of  the  research, 
and  time  will  he  taken  noAv  to  go  into  the  reasons  for 
them  and  also  to  show  some  traces  illustrating  the  condi¬ 
tions  at  Cane  River.  The  influence  of  the  free  air  tem¬ 
perature  in  determining  the  minimum  at  No.  4  is  felt 
under  two  different  types  of  inversion,  the  Intermediate 
and  the  Cyclonic.  In  both  cases  there  occurs  a  gradual 
rise  in  temperature  at  the  top  station,  while  the  tempera¬ 
ture  lower  doAvn  continues  to  fall  from  continued  radia¬ 
tion  A\There  the  freedom  of  air  movement  is  restricted. 
Again,  as  stated  before,  clear  Aveather  with  light  Avind 
is  usually  associated  Avitli  the  Intermediate  Type  and 
increasing  cloudiness  and  Avind  with  the  Cyclonic  Type. 

Under  the  influence  of  a  combination  of  these  two  con¬ 
ditions  there  occurred  at  Cane  River  on  January  27-29, 
1914,  the  most  remarkable  example  of  rising  temperature 


at  a  summit  station  noted  in  the  research,  with  clear 
weather  and  high  pressure  centered  somewhat  to  the  east 
of  the  mountain  region  and  a  deep  low  approaching  from 
the  west  with  a  tendency  toAvard  light  to  moderate  south¬ 
erly  winds,  though  probably  not  enough  to  disturb  the 
calms  in  the  coves  and  valley  floors.  Figure  58  shows 
the  thermograph  traces  during  this  period  at  Nos.  1  and  4. 
From  7  p.  m.  of  the  27th  the  temperature  at  No.  4  rose 
from  46°  to  57°  at  sunrise  of  the  28th,  while  the  tempera¬ 
ture  at  No.  1  fell  continuously  from  a  reading  of  54°  at 
4.00  p.  m.  on  the  27th  to  a  minimum  of  27°  at  sunrise  the 
28th,  thus  producing  an  inversion  of  30°,  the  largest  noted 
at  Cane  River.  On  the  night  of  the  28-29th  there  oc¬ 
curred  an  inversion  of  the  Ideal  Type,  Avhen  the  tempera- 
time  fell  gradually  at  both  top  and  base  stations  during 
the  night,  although  the  fall  at  No.  4  was  retarded  and  did 
not  reach  a  Ioav  point.  On  this  date  there  Avas  an  inver¬ 
sion  of  24°  at  8  a.  m. 

Another  example  of  this  rise  in  temperature  at  the 
summit  station  at  Cane  River,  which  is  entirely  due  to 
the  bringing  in  of  Avarmer  currents  of  air  and  may  be 
considered  a  purely  Cyclonic  Type  of  inversion,  occurred 
during  the  period  December  19-23,  1916,  shoAvn  in 


Fig.  58. — Thermograph  traces,  January  27-29,  1914,  stations  Nos.  1  and  4,  Cane  River. 

Large  inversions. 

Figure  59.  Beginning  Avith  10  p.  m.  on  the  night  of  the 
19th,  the  temperature  rose  continuously  at  No.  4  from 
a  minimum  of  18°  to  a  maximum  of  51°  at  11  a.  m.  on 
the  21st,  or  during  an  interval  of  37  hours,  without  regard 
to  the  usual  diurnal  changes  which  took  place  at  No.  1, 
1,100  feet  below.  During  the  period  from  8  a.  m.  of 
the  19th  to  8  a.  m.  of  the  20th  a  deep  low  moved  rapidly 
southeastward  from  the  middle  Rocky  Mountain  to  the 
lower  Mississippi  Valley,  and  by  the  morning  of  the  21st 
a  trough-like  depression  covered  the  Atlantic  coast  States 
with  the  low  centered  south  of  Alabama.  This  condition 
caused  moderate  and  fresh  southeast  winds  for  a  48- 
hour  period  at  Cane  River.  By  the  morning  of  the  22d 
the  disturbance  had  increased  greatly  in  intensity  and 
was  located  over  the  middle  Atlantic  coast,  with  strong 
northwest  winds  over  the  mountain  region,  resulting  in 
a  norm  condition,  as  shown  by  the  trace.  The  rise  in 
temperature  at  No.  4  during  the  night  of  the  22d-23d 
at  the  same  time  Avhen  there  was  a  gradual  fall  at  No.  1 
is  a  good  example  of  the  Intermediate  Type  of  inversion. 

Still  another  example  of  the  Intermediate  Type  of 
inversion  at  Cane  River  is  found  on  the  night  of  Janu¬ 
ary  3-4,  1916,  illustrated  in  Figure  44,  a  difference  of 
21°  between  Nos.  1  and  4  being  observed  at  8  a.  m.  on 
the  4th,  the  temperature  rising  steadily  at  the  summit 
station  and  falling  at  the  base  from  about  7  p.  m.  of  the 
preceding  day.  On  the  folloAving  night,  owing  to  the 
rapid  approach  of  a  loav,  an  inversion  of  the  Cyclonic 


71 


THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 


Type  occurred,  and  this  condition  is  shown  at  Altapass 
on  the  same  night  in  Figure  54. 

Gorge  and  Globe. — The  slope  at  Gorge  is  quite  unlike 
any  of  the  other  slopes,  the  grade  being  slight  and  the 
slope  long.  Like  Cane  River,  the  highest  temperatures 
in  inversions  are  invariably  found  at  the  summit,  as 
after  No.  2  on  each  slope  is  reached,  the  amount  of  free 
air  in  proportion  to  the  surface  area  continually  becomes 
greater  and  the  minima  higher  and  higher.  Because  the 
elevation  of  No.  5  at  Gorge  is  relatively  low,  the  temper¬ 
ature  of  the  free  air  opposite  it  is  still  high  enough  to 
retard  the  fall  in  temperature  there,  so  that  the  summit 
station  shows  a  higher  reading  than  at  lower  elevations. 

As  station  No.  2  partakes  more  of  the  nature  of  a 
valley  floor  station  because  of  the  large  amount  of  radiat¬ 
ing  surface  in  the  shape  of  surrounding  hills,  which  rise 
to  an  elevation  as  high  as  and  even  higher  than  No.  2, 
and  because  of  the  comparatively  flat  cove-like  location, 
we  find  almost  as  low  readings  here  as  at  No.  1,  as  stated 
previously.  Consequently  marked  inversions  at  Gorge 
are  not  apparent  until  after  No.  2  is  passed,  the  low 
opposing  slopes  cutting  off  any  supply  of  warm  free  air. 


sistently  lower  than  those  at  Globe  during  all  inversion 
periods,  notwithstanding  the  fact  that  Gorge  No.  1  is 
oyer  200  feet  lower  in  altitude,  and  this  is  because  of  the 
difference  in  local  exposure.  Again,  the  readings  at  No. 
2  Gorge  are  always  lower  than  Globe  No.  2  because  of  the 
reat  difference  in  the  surroundings,  the  former  station 
eing  located  in  a  cove  and  surrounded  by  a  large  number 
of  radiating  surfaces  in  the  shape  of  hills,  while  Globe 
No.  2  faces  a  sufficiently  large  volume  of  warm  free  air  to 
prevent  the  temperature  from  reaching  a  low  point  on 
inversion  nights. 

The  differences  between  the  summit  stations  are  small, 
although  in  this  comparison  the  summit  station  at  Gorge 
averages  the  higher  because  of  the  freer  exposure  on  the 
actual  summit  with  small  mass,  while  Globe  No.  3  is  on 
the  summit  of  a  descending  spur  of  Grandfather  Moun¬ 
tain,  which  reaches  northwestward  beyond  and  above 
for  several  miles,  with  increasing  mass  or  surface  area. 

Hendersonville . — The  most  prominent  feature  concern¬ 
ing  the  inversions  in  this  group  is  the  effect  of  wind  di¬ 
rection  and  velocity  as  modified  by  local  topography,  and 
*^Mhis  is  shown  strongly  by  the  average  minimum  tempera- 


However,  the  inversions  in  the  higher  levels  at  Gorge 
are  the  largest  found  on  any  long  slope,  and  this  is 
because  No.  1  is  relatively  cold  for  its  elevation  and  the 
summit  station  No.  5  is  on  a  knob,  where  the  mass  is 
small  and  where  it  faces  an  almost  unlimited  volume  of 
free  air  the  temperature  of  which  is  comparatively  high  on 
account  of  the  low  elevation  of  the  slope  above  sea  level. 

A  most  remarkable  instance  of  large  inversions,  the 
greatest  in  the  entire  four-year  period,  to  which  reference 
has  been  made  before,  occurred  at  6  a.  m.  on  November 
13,  1913,  at  Gorge,  when  a  difference  of  31°  was  noted 
between  Nos.  1  and  5,  the  temperature  rising  at  No.  5 
and  simultaneously  falling  at  No.  1  (see  fig.  75).  This 
condition  was  brought  about  by  a  combination  of  the 
Cyclonic  and  Intermediate  Types  of  inversions. 

As  Globe  and  Gorge  are  only  about  15  miles  apart, 
with  base  stations  within  200  feet  of  the  same  elevation 
above  sea  level,  it  is  interesting  to  note  the  variation  in 
minimum  temperature  during  nights  of  inversion  on 
these  two  slopes  as  affected  by  local  topography,  lhe 
average  minima  at  the  base  station  at  Gorge  are  con- 


tures  for  the  selected  May  period  of  inversion  (Table  2a), 
when  with  calm  nights  or  with  light  southerly  winds 
there  is  an  average  difference  of  9.5°  between  Nos.  2  and 
3,  the  latter  station  being  the  higher.  Occasionally  the 
highest  temperature  is  found  at  No.  2,  and  this  is  solely 
because  of  the  effect  of  northerly  winds.  The  middle  of 
the  thermal  belt  is  usually  found  at  No.  4  and  sometimes 
may  even  be  above  that  station,  at  the  level  of  the  sum¬ 
mit  of  Jump  Off  Mountain,  located  to  the  southwest  and 
nearly  200  feet  higher.  ■  .  . 

This  influence  of  wind  direction  and  velocity  during 
the  November  period  is  brought  out  in  the  discussion  of 
Table  2a,  but  it  does  not  show  strongly  in  the  averages, 
because  on  some  of  the  nights  the  effect  was  only  felt 
during  a  portion  of  the  night.  In  order  to  show  graph¬ 
ically  this  influence,  figure  60  has  been  prepared  showing 
the  superimposed  thermograph  traces  for  two  selected 
periods  in  November,  2d  to  5th  and  19th  to  21st, 
sive,  for  Nos.  1,2,  and  4,  to  which  has  been  appended  the 
houi'ly  wind  direction  and  velocity,  as  recoraed  at  the 
Asheville  Weather  Bureau  station. 


72 


SUPPLEMENT  NO.  19. 


Figure  60  illustrates  the  variation  in  temperature  be¬ 
tween  a  base  and  summit  station  during  a  cold  night 
through  a  subsequent  warm  and  rainy  period  to  another 
cold  night  and  shows  typical  inversions  as  well  as  the 
rapid  recovery  in  temperature  aloft.  Note  the  continu¬ 
ous  rise  in  temperature  at  the  summit  station,  No.  4, 
from  10p.m.,  November  19,  to  11  a. m.,  November  21,  coin¬ 
cident  with  falling  temperature  at  the  base  station,  No.  1, 
during  the  nights  on  these  two  dates. 

It  will  be  recalled  that  Hendersonville  No.  2  is  in  a  cove, 
with  the  air  movement  from  southerly  and  easterly  quar¬ 
ters  much  retarded  by  the  partially  inclosing  forest  areas 
and  the  small  ridge  sheltering  this  cove.  The  stagnation 
of  the  air  movement  on  nights  when  winds  from  these 
directions  blow  results  in  uninterrupted  radiation  through 
out  the  night  with  consequent  low  minima,  while  the 
better  exposure  of  No.  2  with  reference  to  northerly  winds 
tends  to  promote  mixture  of  the  chilled  air  in  the  cove 
with  the  warm  free  air.  The  same  effect  results  when  the 
air  movement  is  very  light,  regardless  of  the  direction  of 
wind.  Thus  on  the  night  of  the  lst-2d,  with  a  light 
northwest  wind,  we  find  the  temperature  at  No.  2  as  high 
or  higher  than  No.  4  at  the  summit  and  from  10°  to  15° 
higher  than  at  No.  1.  On  the  following  night,  during 
intervals  of  light  northwest  wind  and  calm  or  variable 


night  of  the  20th-21st,  when  an  inversion  of  28°  is  noted 
between  Nos.  1  and  4,  the  greatest  observed  at  Hender¬ 
sonville  during  the  period  of  the  research. 

Figure  60  illustrates  the  effect  of  wind  direction  and 
velocity  on  temperature,  especially  noticeable  at  station 
No.  2.  Shaded  portions  of  graph  indicate  the  tempera¬ 
ture  excess,  in  both  time  and  amount,  at  station  No.  4 
over  that  at  No.  2. 

Mount  Airy — The  inversions  at  Mount  Airy  are  not 
large,  taking  the  year  as  a  whole,  and  the  largest  amounts 
by  far  are  found  in  the  unusually  favorable  period  during 
May.  On  one  night  during  the  selected  May  period 
(Table  2a)  of  inversion  there  was  a  difference  of  16° 
between  Nos.  1  and  2,  equivalent  to  an  increase  of  1°  in 
temperature  for  each  10  feet  in  altitude.  It  is  quite 
probable  that  these  large  inversions  in  May  represent 
the  maximum  differences  that  are  possible  on  that  slope. 
Because  of  the  small  elevation  of  this  group  of  stations 
and  the  slight  difference  in  elevation  between  the  sum¬ 
mit  and  the  base  stations,  the  belt  of  highest  temperature 
on  the  west  slope  is  sometimes  at  No. -2  and  sometimes 
reaches  the  summit,  No.  4;  and  on  the  east  slope,  a 
similar  situation  prevails.  When  the  wind  is  from  a 
westerly  direction  the  highest  temperature  is  found  at  No. 
2  instead  of  at  the  summit,  because  large  quantities  of 


Fig.  60. — Thermograph  traces,  November  2-4, 1916,  and  November  19-21,  1913,  stations  Nos.  1,  2,  and  4,  Hendersonville. 


wind,  the  temperature  at  No.  2  fell  and  recovered  fre¬ 
quent!}7,  but  with  an  increased  wind  velocity  from  the 
northwest  shortly  before  sunrise  the  temperature  rose 
slightly  and  equaled  that  at  No.  4.  During  the  evening 
of  the  3d  a  moderate  southeast  wind  prevailed,  but  did 
not  prevent  a  strong  inversion  between  Nos.  1  and  4. 
However,  at  No.  2  we  find  a  remarkable  lowering  of  the 
temperature,  for  a  time  keeping  pace  with  No.  1,  450 
feet  lower.  The  depression  of  the  temperature  at  No.  2 
as  compared  to  No.  1  was  greatest  about  8  p.  m.  with  a 
10-mile-an-hour  wind  from  the  southeast.  Toward 
morning,  with  lessening  wind  velocity,  some  exchange 
with  the  warm  free  air  was  permitted,  and  a  slight  ex¬ 
cess  in  temperature  is  noted  over  station  No.  1,  though 
not  enoiigh  to  prevent  a  heavy  or  killing  frost  at  No.  2. 
Meanwhile  the  temperature  at  No.  4  remained  close  to 
50°,  with  an  average  inversion  of  over  20°  between  Nos. 
4  and  1.  Again,  on  the  following  night,  4th-5th,  a 
light  northwest  wind  followed  by  a  calm  near  midnight 
resulted  in  lowering  the  temperature  at  No.  2,  although  a 
recovery  was  again  noted  with  increase  of  wind  before 
daylight. 

The  influence  of  wind  direction  and  velocity  upon  the 
temperatures  at  Hendersonville  Nos.  2  and  4  is  also  well 
shown  by  the  thermograph  traces  during  the  period 
November  19-21,  1913,  inclusive,  especially  during  the 


warm  free  air  at  a  low  elevation  are  then  brought  to 
this  westerly  slope.  With  all  other  conditions,  the 
highest  temperatures  are  normally  found  at  the  summit. 

The  effect  of  inclination  and  direction  of  slope  is 
shown  by  the  minima  at  Nos.  2  and  3,  the  former  being 
located  on  a  steep  westerly  slope  and  the  latter  on  a 
more  gentle  easterly  slope,  both  stations  having  the  same 
elevation  above  No.  1. 

Figure  61  shows  the  differences  in  temperature  which 
prevail  on  clear  quiet  nights  when,  as  a  result  of  the 
different  topographical  features,  the  minimum  at  No.  2 
may  be  nearly  10°  higher  than  at  No.  3. 

Tryon. — Because  of  the  peculiar  topographical  features 
at  Tryon  (fig.  21),  which  affect  the  now  of  air,  there  are 
some  remarkable  variations  in  the  extent  and  amount 
of  inversions  during  the  course  of  a  year.  Normally,  as 
shown  by  Table  2a,  the  middle  of  the  thermal  belt  lies 
between  Nos.  2  and  3,  at  an  elevation  of  only  400  feet 
above  the  valley  floor.  The  highest  minima  are  usually 
found  at  No.  2.  On  no  other  slope  is  the  center  of  the 
thermal  belt  found  so  close  to  the  valley  floor. 

The  controlling  factor  at  Tryon  in  affecting  inversions, 
both  in  amount  and  extent,  is  the  mountain  breeze, 
which  is  greatly  aided  in  its  development  by  air  move¬ 
ment  from  the  west  down  the  Pacolet  valley.  In  fact, 
this  breeze  is  a  most  vital  factor  in  governing  the  minima 


73 


THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 


^  be  taken  to  discuss  the  subject 

m  detail.  Before  the  beginning  of  the  mountain  breeze  at 


Fig.  61. — Thermograph  traces,  October  11-12,  1916,  stations  Nos.  2  and  3,  Mount  Airy. 
Variation  in  minimum  temperature  due  to  inclination  of  slope. 

night  there  is  an  inversion  along  the  sides  of  the  gorge  of 
the  Pacolet  River  and  the  inclosing  Blue  Ridge,  while 


Blantyre,  and  Bryson,  while  during  the  selected  May 
period  (I  able  2a),  when  the  influence  of  the  mountain 
breeze  at  Iryon  was  unimportant  in  affecting  the  minima, 
the  differences  between  the  Tryon  base  station  and  those 
at  Gorge,  Blantyre,  and  Bryson  are  much  less. 

Again,  we  note  that  at  Tryon  the  summit  station, 
.No.  4,  averages  considerably  higher  as  compared  with 
the  base,  No.  l,in  periods  of  inversion  unfavorable  for  a 
breeze  down  the  slope,  such  as  the  May  period,  than  in 
periods  when  the  breeze  prevails  at  night. 

On  nights  unfavorable  for  the  mountain  breeze  during 
inversion  weather,  the  difference  in  temperature  between 
Nos.  1  and  2  or  between  Nos.  1  and  3  may  equal  or 
exceed  any  inversion  in  the  region.  For  instance,  during 
the  May  period  (Table  2a)  the  largest  individual  inver¬ 
sion  at  Iryon  is  20°  between  Nos.  1  and  2,  differing  in 
elevation  by  380  feet,  while  the  largest  inversion  on  any 
one  night  during  this  period  between  Nos.  1  and  5  at 
Gorge,  these  stations  differing  in  elevation  by  1,040  feet, 
is  but  4°  more.  On  February  18,  1916,  the  inversion 
at  Tryon  was  23°,  which  was  "3°  in  excess  of  any  other 
inversion  in  the  region  the  same  night. 

Figure  62  contains  the  thermograph  traces  at  Tryon 
for  stations  Nos.  1,  2,  and  4  from  noon,  October  27,  to 
noon,  October  31,  1914.  This  period  is  one  of  the  most 
remarkable  found  at  Tryon,  as  the  effects  of  air  move- 


on  the  Saluda  plateau  above  radiation  lowers  the  tem¬ 
perature  so  rapidly  that  there  is  a  cold  blanket  of  air 
in  contact  with  the  warmer  air  on  the  slopes.  As  this 
unstable  condition  can  not  last  long,  the  cold  air  nearest 
the  slopes  finally  breaks  through  the  warm  air  on  the 
slopes  and  forces  the  cold  air  out  of  the  valley  bottom, 
at  the  same  time  warming  itself  by  compression.  This 
often  prevents  low  temperatures  at  No.  1.  Now  when  the 
air  movement  over  the  Saluda  plateau  has  a  westerly 
component,  as  during  anticyclonic  weather,  the  contin¬ 
ual  displacement  of  the  chilled  surface  air  on  the  plateau 
to  a  position  over  the  warm  air  on  the  sides  of  the  gorge 
gives  a  constant  impetus  to  the  movement  of  the  moun¬ 
tain  breeze,  and  under  such  conditions  the  temperature 
remains  high  at  No.  1  during  the  entire  night,  while  in 
other  valleys  at  the  same  elevation  and  under  the  same 
weather  conditions,  but  uninfluenced  by  a  breeze,  the 
temperature  may  be  from  10°  to  20°  lower.  I  his  ac¬ 
counts  for  the  fact  that  inversions  may  occur  on  other 
slopes  when  conditions  approaching  a  norm  are  noted 
at  Tryon.  Thus  we  find  the  average  minima  at  Tryon 
No.  1  during  the  November  period  (Table  2a)  when  the 
breeze  was  quite  marked,  much  higher  than  observed  at 
all  other  typical  valley-floor  stations,  such  as  Gorge, 


ment  combined  with  the  peculiar  topographical  features 
are  excellently  illustrated  by  the  thermograph  sheets  for 
the  nights  of  the  period  mentioned  above;  in  fact,  during 
the  three  nights  beginning  with  that  of  the  28th-29th, 
the  effect  upon  the  temperatures  at  Nos.  1,  2,  and  4  of 
light  easterly  winds,  moderate  westerly  winds,  and  light 
westerly  winds  are  successively  shown,  and  the  vertical 
temperature  gradients  on  the  Tryon  slope  at  midnight 
of  these  three  nights  are  illustrated  by  curves  in  Figure  64, 
the  adiabatic  gradient  being  represented  by  the  straight 
line  at  the  left.  These  two  graphs  are  discussed  in  the 
following  paragraphs. 

The  weather  was  clear  each  night  of  this  selected 
October  period  at  Tryon  (fig.  62),  and  during  the  greater 
portion  of  the  night  of  the  27th-28th,  under  the  influence 
of  diminishing  northwest  winds,  the  temperature  at  No.  4 
was  the  lowest  on  the  slope.  So  long  as  there  was  any 
force  at  all  to  the  wind,  the  temperature  at  No.  1  was 
prevented  from  falling  to  a  low  point,  but  as  soon  as  the 
wind  diminished  the  temperature  on  the  valley  floor 
became  almost  as  low  as  that  at  No.  4.  This  condition, 
however,, did  not  occur  until  about  i  a.  m.  on  the  28th. 
On  the  night  of  the  28-29th,  the  wind  changed  to  light 
southeast  and  east,  causing  a  moderate  inversion,  which 


74 


SUPPLEMENT  NO.  19. 


resulted  in  reducing  the  minimum  at  No.  1  to  a  point  12° 
lower  than  No.  2  and  10°  lower  than  No.  4.  The  vertical 
temperature  gradient  at  midnight  is  shown  in  Figure  63 
by  the  curve  marked  “Light  easterly  winds.”  Note  the 
rapid  fall  in  temperature  at  No.  1  in  the  graph  (fig.  62) 
during  this  night  as  compared  with  the  gradual  fall  at 
the  same  station  on  the  preceding  night,  when  the  falling 
curves  of  temperature  at  both  Nos.  1  and  4  are  nearly 
parallel  until  about  6  a.  m. 

The  thermal  belt  at  Tryon  is  built  up  to  an  unusual 
height  on  inversion  nights  during  the  prevalence  of  light 
southeast  or  southerly  winds,  as  the  cold  air  is  then 
pocketed  in  the  gorge  above  No.  1  and  is  only  slightly 
disturbed  by  the  moderate  flow  of  air  above  it.  No.  1 
then  continues  to  lose  heat  by  radiation  until  a  con¬ 
siderable  inversion  is  formed,  as,  of  course,  the  tempera¬ 
ture  at  Nos.  2,  3,  and  4  is,  under  these  conditions,  quite 
high,  the  slope  being  warmed  by  the  free  air  brought  to  it 
by  the  southeasterly  winds.  At  these  times,  the  highest 
temperature  is  often  found  at  No.  4  or  even  on  the  very 
summit  of  Warrior  Mountain,  400  feet  above  No.  4  and 
over  1,000  feet  above  No.  2,  where  the  center  of  the 
thermal  belt  on  this  mountain  is  usually  found,  showing 
that  under  the  most  favorable  conditions  the  thermal 
belt  at  Tryon  reaches  to  a  considerable  height. 


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Fig.  63. — Vertical  temperature  gradients  under  varying  conditions,  October  29-31, 1914. 

Returning  now  to  the  discussion  of  Figures  62  and  63, 
it  is  noted  that  in  the  former  a  sudden  fall  in  tempera¬ 
ture  occurred  at  No.  1  on  the  29th,  shortly  after  4  p.  m. 
This  drop  was  caused  by  a  change  in  the  direction  of  the 
wind  to  the  northwest.  During  the  night  of  the  29th- 
30th  the  northwest  winds  increased  in  velocity,  thus  aid¬ 
ing  in  the  development  of  the  mountain  breeze,  which 
caused  a  sharp  rise  in  temperature  at  No.  1  at  10  p.  m. 
Moreover,  the  general  westerly  movement  of  the  air  was 
of  such  strength  during  the  night  that  a  cold  descending 
current  from  the  Saluda  plateau  was  felt  at  the  other 
stations,  especially  at  No.  4,  where  the  hourly  readings 
were  unusually  low  during  most  of  the  night.  On  clear 
nights,  such  as  the  one  in  question,  with  the  breeze  blowing 
at  No.  1,  it  is  often  noticed  that  No.  4  is  much  too  cola 
considering  the  difference  in  elevation,  and  this  is  prob¬ 
ably  accounted  for  by  the  fact  that  the  general  air  move¬ 
ment  from  a  westerly  direction,  which  seems  necessary 
for  the  full  development  of  the  mountain  breeze,  de¬ 
scends  through  the  warmer  air  on  the  eastern  slope  of 
Warrior  Mountain  and  reduces  the  temperature  on  the 
slope,  although  being  warmed  itself  by  the  same  process. 
The  weight  of  the  descending  cold  air  mixing  with  the 
previously  warm  air  on  the  slopes,  forces  it  downward, 


which  in  turn,  from  the  pressure  behind  it,  displaces  the 
cold  air  at  the  bottom  of  the  valley,  and  it  is  only  under 
these  conditions — that  is,  when  the  air  movement  from 
the  west  is  strong  enough  to  push  the  cold  surface  air  of 
the  plateau  over  the  summit  of  Warrior  Mountain — that 
a  descending  air  current  is  felt  at  all  three  stations,  Nos. 
2,  3  and  4.  This  combination  of  a  strong  mountain 
breeze  at  No.  1  and  strong  descending  currents  down  the 
slope  of  Warrior  Mountain  occurs  only  infrequently  and 
is  seldom  shown  by  the  minima  at  the  slope  stations, 
Nos.  2  and  3.  While  the  influence  of  the  mountain 
breeze  passing  down  the  gorge  of  the  Pacolet  prevents 
the  temperature  from  falling  at  No.  1,  and  even  causes 
it  to  rise,  the  cold  air  descending  from  the  plateau  down 
the  slope  of  Warrior  Mountain  is  not  sufficiently  warmed 
through  compression  to  prevent  the  temperature  there 
from  falling.  This  combination  is  only  temporary  and 
generally  lasts  but  a  few  hours.  An  excellent  example 
of  this  condition  is  shown  in  Figure  62  on  the  night  under 
discussion,  October  29-30,  when  from  11  p.  m.  to  4  a.  m., 
the  temperature  at  No.  2,  the  center  of  the  thermal  belt, 
was  continually  lower  than  No.  1  at  the  hour  of  3  a.  m., 
the  difference  being  nearly  5°.  After  this  hour  the  wind 
diminished,  and  the  temperature  at  No.  1  therefore  fell 
to  a  point  below  No.  2.  The  vertical  temperature  gra¬ 
dient  on  this  same  night  at  midnight  is  shown  in  Figure 
63  by  the  black  line  marked  “Moderate  westerly  winds,” 
which  closely  follows  the  adiabatic  gradient  represented 
at  the  left  by  the  straight  line.  These  descending  cur¬ 
rents  on  Mount  Warrior  have  little  or  no  effect  upon  the 
temperature  at  No.  1,  which  is  entirely  under  the  influ¬ 
ence  of  the  brisk  wind  which  sweeps  out  from  the  gorge 
of  the  Pacolet  valley,  the  temperature  of  the  valley  floor 
being  regulated  by  conditions  which  differ  widely  from 
those  on  the  steep  easterly  slope  of  Warrior.  For  these 
reasons  it  is  rather  difficult  to  compare  No.  1  on  the 
valley  floor  with  the  three  upper  stations  on  the  slope. 
If  the  upper  stations  were  situated  in  the  gorge  of  the 
Pacolet  in  a  line  with  No.  1,  we  would  often  find  a  gradual 
decrease  in  temperature  with  elevation,  but  instead  they 
are  located  in  a  sheltered  position  on  the  eastern  wall  of 
the  inclosing  Blue  Ridge  and  normally  little  affected  by 
the  breeze. 

After  the  mountain  breeze  is  fully  developed,  the 
considerable  mixing  of  the  air  will  give  a  vertical  tem¬ 
perature  gradient  on  the  slope  corresponding  nearly  to 
the  adiabatic  rate,  as  brought  out  in  the  preceding 
paragraph,  but  as  the  temperature  falls  lower  ana 
lower  on  the  Saluda  plateau  as  the  night  proceeds,  this 
flow  of  cold  air  descending  the  slope  gradually  lowers 
the  temperature  at  No.  4  at  a  corresponding  rate.  But 
since  the  volume  of  cold  air  forcea  over  the  edge  of 
the  plateau  is  small  when  light  westerly  winds  prevail, 
it  does  not  descend  the  slope  of  Warrior  Mountain  in 
sufficient  quantity  to  force  its  way  to  the  bottom; 
hence  the  temperature  at  only  Nos.  4  and  3  is  lowered, 
the  readings  at  the  latter  station  being  but  slightly 
affected,  while  the  relation  of  the  minima  at  Nos.  2 
and  1  is  similar  to  that  under  inversion  conditions, 
except  that  the  reading  at  the  latter  station  is  rela¬ 
tively  high.  Thus  at  sunrise,  for  instance,  the  tem¬ 
perature  gradient  may  be  strongly  superadiabatic,  and 
this  relation,  especially  between  Nos.  2  and  4,  is  not 
uncommon  at  any  hour  of  the  night.  It  is  well  shown 
in  figure  63  by  the  black  line  marked  “Light  westerly 
winds,”  which  represents  the  gradient  at  midnight  of 
October  30-31.  During  this  night  a  true  mountain 
breeze  prevailed,  with  light  westerly  winds,  and  the 
temperature  at  No.  1  fluctuated  considerably,  although 


THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 


75 


with  a  falling  tendency,  but  it  was  undoubtedly  pre¬ 
vented  from  falling  to  as  low  a  point  as  it  otherwise 
would  had  no  breeze  occurred.  In  figure  62,  note  the 
relatively  high  temperature  at  No.  2  as  compared  with 
the  readings  at  both  Nos.  1  and  4  on  that  night,  result¬ 
ing  in  the  marked  superadiabatic  gradient^  shown  in 
figure  63. 

Isopleths  showing  progressive  distribution  of  tempera¬ 
ture  during  a  May  period  of  inversion  at  Ellijay .—The 
isopleth  (fig.  64)  shows  the  progressive  distribution  of 
average  temperature  on  the  slope  at  Ellijay  during  a 
typical  six-day  period  in  May,  1914.  During  the  day¬ 
light  hours  we  find  a  normal  decrease  in  temperature 
due  to  elevation  continuing  until  abbut  5  p.  m.,  when 
the  sun  s  rays  are  shut  off  at  station  No.  1  by  intervening 
mountains,  although  they  are  still  effective  on  the  re^ 
mainder  ol  the  slope.  A  rapid  loss  in  heat  occurs  at 
this  time  at  No.  1  and  a  loss  also,  although  in  a  much 
less  degree,  at  Nos.  4  and  5,  while  the  more  effective 
insolation  at  Nos.  2  and  3  delays  the  rapid  fall  in  tem¬ 
perature  at  those  stations — in  fact,  nearly  an  hour  in 
the  case  of  No.  2.  The  point  of  highest  temperature 
appears  successively  at  the  stations  in  order  of  their 


versions.  If  the  weather  conditions  are  stable  and  purely 
anticyclonic  and  the  absolute  humidity  low,  the  suc¬ 
cessive  appearances  of  this  relatively  warm  belt  at  in¬ 
creasing  elevations  are  so  rapid  that  they  are  difficult  to 
follow,  but  during  more  humid  weather  the  change  can 
be  traced  quite  easily,  and  often  the  rising  sun  of  the 
following  morning  finds  the  belt  below  the  normal  height 
(see  Table  17). 

Mean  minimum  temperatures  during  inversion  weather 
at  14  base  stations  corrected  for  latitude  and  to  the  2,000- 
foot  level. — We  have  seen  in  the  preceding  paragraphs  the 
marked  influences  of  topography  during  nights  of  inver¬ 
sion,  resulting  in  great  differences  in  minima  at  points 
having  approximately  the  same  elevation.  Some  base 
stations  are  relatively  colder  than  others,  just  as  there 
are  variations  between  the  minima  at  slope  stations  and 
between  those  at  summit  stations.  The  temperature  at 
the  summit  depends  largely  upon  the  surrounding  surface 
area,  and  that  on  the  slope  upon  its  direction  and  steep¬ 
ness,  as  well  as  the  proximity  to  opposing  slopes.  How¬ 
ever,  there  is  naturally  a  difference  of  opinion  as  to  the 
kind  of  base  station  that  insures  the  lowest  minima 
during  nights  of  inversion.  The  term  “ frost  pocket”  is 


increase  in  elevation,  but  during  this  period  it  never 
reaches  No.  5.  However,  more  complete  observations 
on  the  slope,  if  available,  would  undoubtedly  show 
that  the  average  highest  minima  during  the  week  in 
question  occurred  at  a  point  about  midway  between  Nos. 
4  and  5.  This  successive  rise  in  the  position  of  highest 
minima  with  increasing  elevation  is  partially  due  to 
the  shutting  off  of  the  sun’s  rays,  but  mainly  to  the 
reshaping  of  the  vertical  temperature  gradient  with  the 
more  rapid  loss  in  heat  at  the  lower  stations. 

About  4:30  a.  m.  the  largest  inversion  occurs,  averaging 
15.8°  between  Nos.  1  and  4.  Note  the  rapid  rise  in 
temperature  during  the  early  morning  hours  at  the 
lower  stations,  especially  at  No.  1,  the  temperature  at 
the  base  reaching  about  the  same  degree  as  at  No.  5 
shortly  before  8  a.  m.,  at  which  hour  the  temperature 
averages  about  6°  lower  at  No.  2  than  at  No.  1.  No.  2  is 
the  last  station  at  which  the  temperature  begins  to  rise 
in  the  morning,  because  the  sun’s  rays  reach  this  location 
on  the  slope  later  than  at  any  other  point.  By  9  a.  m. 
the  normal  decrease  in  temperature  with  elevation  pre¬ 
vails,  this  continuing  until  the  late  afternoon,  when  the 
same  processes  are  repeated  on  nights  favorable  for  in- 


often  used  without  any  special  reference  to  the  character 
of  the  surrounding  topography,  and  the  fact  that  low 
minima  occur  at  such  a  place,  with  resulting  serious 
damage  during  frosty  nights,  is  usually  considered  suffi¬ 
cient  to  justify  the  appellation.  lioAvever,  there  are 
different  kinds  of  frost  pockets,  and  an  attempt  will  be 
made  here  to  point  out  the  features  that  have  the  most 
important  bearing  upon  the  situation. 

In  Table  19,  used  in  this  comparison,  a  correction  has 
been  applied  to  the  base  station  readings  for  both  eleva¬ 
tion  and  latitude,  the  stations  being  reduced  to  a  com¬ 
mon  base  of  2,000  feet  above  sea  level,  and  to  a  latitude 
of  35°  north.  The  elevation  of  2,000  feet  is  selected,  as 
that  represents  approximately  the  average  of  all  the 
base  stations  employed  in  the  research,  and  the  parallel 
35°  passes  along  the  southern  border  of  the  region. 

In  order  to  make  the  reductions  for  elevation,  a  cor¬ 
rection  of  1°  for  each  300  feet  has  been  applied  to  the 
observed  minima.  The  vertical  temperature  gradient 
is  greater  in  summer  than  in  winter,  so  that  the  correc¬ 
tion  of  1°  for  300  feet  is  probably  insufficient  during  the 
warmer  months  of  the  year,  too  large  for  the  winter 
months,  and  near  the  true  correction  for  the  spring  and 


30442—23 - 6 


76 


SUPPLEMENT  NO.  19. 


autumn  months  and  for  the  year  as  a  whole.  The  cor¬ 
rection  for  latitude  applied  varies  with  the  season  of  the 
year,  at  the  more  northerly  points  approximately  1.2° 
in  summer,  2°  in  spring  and  autumn,  3°  in  winter,  and 
2°  for  the  means  of  all  four  seasons,  which  represent 
annual  values.  In  contrast  with  these  the  more  south¬ 
erly  stations  have  practically  no  corrections  for  latitude, 
while  those  midway  have  intermediate  values.  Reduc¬ 
tions  of  this  kind  can  not  be  made  with  any  refinement, 
but  it  is  thought  that  the  comparison  would  not  be 
satisfactory  without  some  correction,  so  as  to  reduce 
approximately  the  readings  to  a  common  basis. 

For  the  purposes  of  this  comparison  periods  of  inver¬ 
sion  are  selected  for  each  month  of  the  year,  as  well  as 
extra  periods  for  May  and  November,  double  weight 
being  given  to  these  months  on  account  of  the  greater 
frequency  of  inversions.  Table  19,  which  contains  these 
values,  furnishes  most  interesting  results.  In  the  spring, 
summer,  and  autumn  the  base  stations  at  Highlands, 
Bryson,  and  Blantyre  are  seen  to  be  the  coldest,  the 
Highlands  station  being  especially  the  coldest  in  the 
summer.  This  station  is  located  in  the  saucer-shaped 
depression  so  often  referred  to,  with  a  slope  to  the  north¬ 
west  on  which  the  orchard  stands,  and  dense  surround¬ 
ing  timber  in  all  other  directions.  The  situation  is  such 
at  this  point  that  there  is  practically  no  opportunity  for 
interchange  with  the  warm  free  air,  nor  is  there  ever  a 
mountain  breeze  possible  from  the  slope  above  during 
nights  of  inversion.  Moreover,  during  the  seasons  of  the 
year  when  the  foliage  is  dense,  especially  in  summer,  the 
air  is  trapped  by  the  dense  timber,  and  the  cold  air 
accumulates  in  large  quantities.  While  Highlands  No.  3 
appears  in  Table  19  as  the  coldest  of  the  base  stations 
during  spring,  summer,  and  autumn  inversions,  several 
base  stations  in  winter  have  lower  corrected  minima. 
The  trees  in  the  vicinity  of  the  Highland  station  are 
deciduous,  and  the  frost  pocket  is  therefore  not  so  pro¬ 
nounced  in  the  winter,  as  the  timber  then  does  not  serve 
as  a  barrier  to  the  movement  of  air  out  of  the  pocket,  as 
it  does  in  summer.  The  situation  at  Bryson  and  Blan¬ 
tyre,  the  two  other  base  stations  having  abnormally  low 
minima,  is  much  different  from  that  at  Highlands. 
Bryson  and  Blantyre  are  both  situated  close  to  wide 
valley  floors,  where  the  air  movement  is  reduced  by  sur¬ 
rounding  mountains,  but  not  close  enough  to  interfere 
with  radiation,  and  with  considerable  marsh  land  and 
dense  vegetation  surrounding,  from  which  loss  of  heat 
by  radiation  is  rapid  during  nights  of  inversion.  There 
is,  in  fact,  no  obstruction  to  radiation  at  either  of 
these  two  base  stations,  and  doubtless  on  the  very  floor 
of  the  valley  at  Blantyre  the  minima  would  be  even 
lower  than  at  station  No.  1,  which  is  slightly  above  on  a 
terrace.  Thus  we  have  a  small  frost  pocket  at  High¬ 
lands  and  large  ones  at  Bryson  and  Blantyre  of  an 
entirely  different  character,  but  which  may  nevertheless 
be  called  true  frost  pockets  in  spite  of  their  large  area. 

Gorge  and  Ellijay,  moreover,  are  rather  cold  points, 
and  while  the  topography  at  these  two  places  is  much 
unlike  that  at  Highlands,  Bryson,  and  Blantyre,  where 
the  lowest  temperatures  of  the  entire  region  are  regis¬ 
tered,  the  low  minima  at  Gorge  and  Ellijay  are  due 
largely  to  stagnation,  having  higher  elevations  in  close 
proximity  on  all  sides,  although  this  condition  serves 
at  the  same  time  to  limit  the  opportunities  for  free 
radiation.  Again,  at  the  summits  of  these  five  slopes, 
all  of  which  culminate  in  knobs,  the  surface  area  is  not 
great,  and  there  is  no  development  of  a  mountain  breeze 
downward,  with  consequent  rise  in  temperature  on  the 
valley  floors,  as  may  be  found  at  Tryon  and  Blowing 


Rock,  for  instance.  Blowing  Rock  No.  3,  while  often 
referred  to  as  a  frost  pocket  having  consistently  low 
temperatures  throughout  the  year  because  of  its  eleva¬ 
tion,  nevertheless  is  so  frequently  favored  by  a  breeze 
at  night  during  periods  of  inversion  that  its  minima 
average  much  higher  than  other  stations  where  conditions 
would  seem  more  favorable.  Along  the  summit  of  the 
orchard  in  which  No.  3  is  located  there  is  a  considerable 
area,  and  below  the  station  there  is  an  outlet,  thus  per¬ 
mitting  the  breeze  to  pass  down  the  valley  of  the  New 
River  and  thus  raising  the  temperature  mechanically  at 
the  valley  floor  station. 

During  inversion  nights  unfavorable  for  the  breeze  at 
Blowing  Rock,  when  the  trend  of  the  air  is  from  the 
southeast,  minima  are  observed  at  station  No.  3  as  low 
as  at  any  base  station  in  the  entire  region  and  sometimes 
even  lower  and  it  is  only  because  of  the  breeze  during 
certain  nights  that  the  average  minima  there  are  so  high 
as  compared  with  those  at  other  base  stations. 

The  base  stations  not  located  on  true  valley  floors, 
such  as  those  at  Transon,  Asheville,  and  Mount  Airy, 
have  the  highest  corrected  minima,  if  Blowing  Rock  and 
Tryon  be  excepted.  The  Tryon  station,  of  course,  has  a 
osition  on  a  true  valley  floor,  but  its  comparatively 
igh  minima  are  due  to  the  night  breeze,  as  previously 
described,  and  also  to  the  relatively  greater  vapor  pres¬ 
sure  in  its  lower  position. 

Table  19  certainly  shows  great  variation  in  these  cor¬ 
rected  minima.  Bryson  for  both  the  year  and  the  winter 
season  has  the  lowest  minima  and  Mount  Airy  the 
highest,  with  average  differences  between  them,  re¬ 
spectively,  of  9.8°  and  9.7°.  Highlands  has  the  lowest 
in  the  spring,  summer,  and  autumn,  as  stated  previously, 
Mount  Airy  the  highest  in  spring  and  autumn,  and  Tryon 
the  highest  in  summer,  Highlands  averaging  12.3°  lower 
in  spring  and  autumn  and  12.6°  in  summer.  These 
large  differences  in  temperature  fairly  represent  the 
varying  effect  of  topography  and  vegetation  and  in¬ 
dicate  that  there  are  great  variations  in  base  station 
readings  of  the  same  elevation  and  latitude. 

Table  19. — Average  minimum  temperatures  during  inversion  weatlier 

at  14  base  stations,  corrected  for  latitude  and  to  the  2,000-foot  level. 


[The  temperatures  are  corrected  for  latitude  35°  north.  In  reducing  for  elovation  1°  is 
allowed  for  each  300  feet  of  increase  in  elevation.  The  elevation  of  2,000  feet  represents 
approximately  the  average  elevation  of  the  14  base  stations  used  in  the  table.] 


Order. 

Station. 

Temper¬ 

ature. 

Order. 

Station. 

Temper¬ 

ature. 

SPRING  AND  FALL. 

WINTER 

1 

No.  3,  Highlands . 

36.4 

1 

24.1 

2 

No.  1,  Bryson  City. . .. 

37.5 

2 

No.  1,  Blantyre. . 

24.4 

3 

No.  1,  Blantyre . 

37.6 

3 

No.  1,  Gorge . 

26. 1 

4 

No.  1,  Hendersonville  . 

39.3 

4 

No.  1,  Ellifay . 

26.7 

5 

No.  1,  Gorge . 

39.5 

5 

No.  1,  Hendersonville . . . 

27.2 

6 

No.  1,  Cane  River . 

39.5 

6 

No.  3,  Highlands . 

27.5 

7 

No.  1,  Ellijay . 

39.9 

7 

No.  1,  Cane  River . 

27.2 

8 

No.  1,  Wilkesboro . 

43.0 

8 

28.6 

9 

No.  1,  Transon . 

43.6 

9 

No.  1,  Globe . 

29.7 

10 

No.  1,  Globe . 

44.0 

10 

29.8 

u 

No.  1,  Asheville . 

44.9 

ii 

No.  1,  Transon . 

32.3 

12 

No.  1,  Tryon . 

45.5 

12 

No.  3,  Blowing  Rock _ 

33.0 

13 

No.  3,  Blowing  Rock.  . 

45.7 

13 

No.  1,  Asheville . 

33.0 

14 

No.  1,  Mount  Airy. 

48.7 

14 

No.  1,  Mount  Airy . 

33.8 

SUMMER. 

ANNUAL. 

i 

No.  3,  Highlands .... 

46.8 

i 

No.  1,  Bryson  City . 

36. 1 

2 

No.  1,  Bryson  City. . . . 

49.4 

2 

No.  3]  Highlands.". . 

36.2 

3 

No.  1,  Blantyre . 

49.8 

3 

No.  1,  Blantyre . 

36.  4 

4 

No.  1,  Ellijay . 

49.9 

4 

No.  1,  Gorge". . 

38.0 

5 

No.  1,  Cane  Stiver . 

50.4 

5 

No.  1,  Ellijay . 

38.0 

6 

No.  1,  Hendersonville.. 

51.0 

6 

No.  1,  Cane  River . 

38.3 

7 

No.  1,  Gorge . 

51.3 

7 

No.  1,  Henderson \ille. .. 

38.3 

8 

No.  1,  Transon . 

52.9 

8 

40.  4 

9 

No.  Wilkesboro . 

53.9 

9 

No.  1,  Globe . 

41.7 

10 

No.  1,  Asheville . 

53.9 

10 

42. 1 

11 

No.  1,  Globe . 

54.0 

11 

43.2 

12 

No.  3,  Blowing  Rock.  . 

55.4 

12 

No.  1,  Tryon . 

43.8 

13 

No.  1,  Mount  Airy . 

58.1 

13 

No.  3,  Blowing  Rock _ 

43.9 

14 

No.  1,  Tryon . 

59.4 

14 

No.  1,  Mount  Airy . 

45.9 

THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 


Approximate  vertical  temperature  gradients  during  typical 
periods  of  inversion.  The  graph  (fig.  65)  shows  the  ap¬ 
proximate  vertical  temperature  gradients  of  the  free  air 
over  a  plain  as  constructed  from  the  average  minimum 
temperatures  for  the  two  periods  of  typical  inversion 
weather,  May  1-6,  1913,  and  November  2-5,  1916,  used 
in  Table  2a.  The  free-air  curves  are  represented  by  the 
two  heavy  black  lines  at  the  right  and  are  based  upon 
data  for  the  following  summit  or  high  slope  stations: 


Stations. 

May 

period. 

November 

period. 

Mount  Airy  No.  4 . 

A 

A' 

Gorge  No.  5 . 

B 

B' 

Globe  No.  3 . 

c 

C' 

Hendersonville  No.  4 . 

D 

D' 

Transon  No.  4 . 

E 

E' 

Ellijay . 

F 

F' 

Ellijay  No.  5 . 

F" 

Cane  ttiver  No.  4 . 

G 

G' 

Highlands  No.  5 . 

H 

H' 

ascent)  and  the  adiabatic  gradient  (1.6°  for  each  300  feet) 
are  shown  by  the  dotted  lines  for  comparative  purposes 
in  connection  with  the  temperature  gradients  on  the 
selected  slopes. 

The  individual  vertical  temperature  gradients  for 
seven  selected  slopes,  including  that  in  the  Waldheim 
orchard  at  Highlands,  for  both  periods,  May  and  Novem¬ 
ber,  are  shown  in  the  graph  at  the  left  of  the  free-air 
curves  and  are  illustrated  by  lighter  curved  lines.  These 
gradients  are  most  interesting,  and,  although  there  is  a 
marked  similarity  in  the  May  and  November  curves,  the 
differences  are  due  to  differences  in  the  direction  of  the 
air  movement  prevailing  during  the  periods  selected. 

In  calm  anticyclonic  weather  the  mountain  breeze  is 
the  rule  at  Tryon,  although  some  periods  are  more 
favorable  for  its  development  than  others.  The  May 
period  selected  is  slightly  unfavorable  in  that  light 
southeast  to  south  winds  prevailed  on  the  nights  selected, 


These  stations  are  selected  as  representing,  within  5°  or 
so,  the  temperature  of  the  free  air  on  inversion  nights  at 
their  respective  elevations.  The  free-air  curves  for  each 
period  are  drawn  from  the  base  station  at  Tryon,  but  as 
the  average  for  this  elevation  does  not  represent  a  typical 
reading  on  account  of  the  frequency  of  the  mountain 
breeze  the  average  minimum  temperature  for  Gorge  No.  1, 
reduced  to  that  elevation,  is  used  as  the  surface  tempera¬ 
ture  for  that  altitude. 

These  curves  have  been  drawn  somewhat  to  the  right 
with  reference  to  the  selected  stations,  since  even  the  most 
ideal  slope  station  during  a  night  of  inversion  would  have 
a  lower  temperature  than  the  adjacent  free  air. 

At  the  left  in  the  graph  the  normal  decrease  in  temper¬ 
ature  with  elevation  in  free  air  (1°  for  each  300  feet  of 


thus  having  a  tendency  to  hold  back  the-  accumulated 
cold  air  on  the  plateau.  The  November  period  happens 
to  be  extremely  favorable,  with  a  predominance  of  air 
movement  from  the  northwest.  The  curve  for  the  May 
period,  therefore,  more  nearly  resembles  the  heavy  curve, 
while  the  November  gradient  is  strongly  superadiabatic 
after  passing  No.  2,  with  the  waterlike  descent  of  cold 
air  on  No.  4  from  the  plateau  above. 

The  two  curves  for  Globe  differ  considerably,  the  tem¬ 
perature  of  No.  1  during  the  November  period  being 
unusually  high  for  its  elevation.  The  position  of  this 
station  is  well  located  topographically  to  experience  a 
mountain  breeze,  yet  the  actual  occurrence  of  the 
breeze  is  both  infrequent  and  of  short  duration.  It  is 
also  not  a  typical  valley-floor  station  in  that  the  profile 


78 


SUPPLEMENT  NO.  19. 


of  Gragg  Fork,  where  the  station  is  located,  shows  a 
considerable  inclination  as  compared  with  that  of  the 
valley  floor  at  Gorge,  for  instance,  Globe  No.  1  having  a 
better  air  exchange  than  most  valley  floor  stations. 
Again,  the  available  sky  room  for  radiation  is  consider¬ 
ably  cut  down  by  the  near  approach  of  the  opposing  steep 
slopes. 

The  curves  at  Gorge  are  irregular  and  of  unusual  con¬ 
tour,  and  this  is  because  of  the  unusually  low  tempera¬ 
tures  at  the  lower  stations  due  to  the  confining  walls, 
while  the  minima  at  the  upper  stations  are  high. 

The  curves  for  Altapass  for  May  and  November  are 
much  alike,  but  quite  dissimilar  to  the  free-air  curve. 
The  five  stations  here  are  on  a  steep  slope  near  a  gorge 
which  has  been  cut  back  into  the  Blue  Ridge  plateau, 
so  that  on  a  calm  clear  night  we  find  a  great  accumula¬ 
tion  of  cold  air  over  the  plateau  and  directly  over  the 
slope  on  which  the  orchard  stations  are  located.  The 
descent  and  mixing  of  this  cold  air  with  the  warm  free 


Fig.  66. — Average  position  of  thermal  belt  on  six  long  slopes  during  typical  inversion 

weather. 


air  in  the  valley  reduces  the  temperature  of  the  whole 
slope,  and  although  the  usual  thermal  conditions  are  dis¬ 
played  on  the  slope,  yet  there  is  a  considerable  reduction 
of  the  temperature  on  the  entire  slope,  referred  to  on  a 
previous  page.  If  these  curves  were  continued  below 
station  No.  1  to  substation  No.  la,  they  would  be  ap¬ 
proximately  parallel  to  those  at  Gorge. 

For  both  periods  at  Cane  River  the  curves  are  quite 
similar,  except  that  in  the  November  period,  the  tem¬ 
perature  at  No.  4  appears  relatively  lower  than  in  May 
because  of  the  prevailing  northerly*  winds  in  November, 
which  serve  to  bring  warm  free  air  to  the  slope  stations 
lower  down. 

r  At  Ellijay  the  summit  station  was  not  in  operation  in 
May,  1913,  so  that  the  complete  curve  for  the  selected 
period  in  that  month  is  not  shown,  but  in  the  autumn 
period  the  curve  is  ideal  after  No.  3  is  reached,  as  then  the 
temperature  of  the  slope  partakes  more  and  more  of  that 
of  the  free  air  which  at  the  elevations  of  Nos.  4  and  5  is 
available  in  large  quantities  with  decreasing  surface  area. 

The  curves  at  Highlands  naturally  show  the  markedly 
low  temperatures  prevailing  at  the  base  station,  No.  3, 
in  the  Waldheim  orchard  and  the  large  differences  be¬ 


tween  it  and  No.  4,  and  are  quite  similar  for  both  selected 
periods,  as  wind  direction  and  velocity  have  no  effect 
upon  the  temperature  conditions  on  this  slope. 

The  vertical  temperature  gradient  is  more  nearly  adi¬ 
abatic  in  summer  than  in  winter,  and  the  constructed 
free-air  curves  shown  in  Figure  65  for  the  May  and 
November  periods  conform  to  this  seasonal  difference. 

HEIGHT  OF  THERMAL  BELT. 

Average  position  of  the  center  of  thermal  belt  on  nights 
of  inversion. — Figure  66  shows  the  average  position  of  the 
belt  of  highest  temperature  on  typical  nights  of  inversion 
on  the  six  slopes  having  a  range  in  vertical  height  from 
1,000  to  1,760  feet,  Altapass,  Cane  River,  Ellijay,  Globe, 
Gorge,  and  Tryon.  In  this  figure  the  shaded  columns 
represent  the  vertical  height  of  the  various  slopes  and 
their  relative  elevation.  The  circle  marked  “T.  B.”  in¬ 
dicates  the  average  position  of  the  thermal  belt  during 
typical  periods  of  inversion  weather.  The  density  of 
shading  shows  the  relative  warmth  on  various  portions 
of  the  slopes.  The  Altapass  slope  in  the  figure  includes 
not  only  the  five  experimental  stations,  but  also  the  re¬ 
mainder  of  the  slope  below  station  No.  1  down  to  the 
valley  floor  at  No.  la,  conforming  to  the  plan  discussed 
on  a  former  page,  when  a  comparison  of  thermal  condi¬ 
tions  was  made  between  Altapass  and  Ellijay. 

The  main  factors  determining  the  height  of  this  belt 
are  the  inclination  or  grade  of  the  slope  and  the  surface 
area  at  the  summit.  The  direction  of  ah’  movement  is 
often  quite  important,  as,  generally  speaking,  exchange 
between  the  slope  and  the  warm  free  air  facing  it  is  hin¬ 
dered  on  the  lee  side  and  aided  on  the  windward  sides, 
cold  air  accumulating  on  the  slope  on  the  lee  side,  with  a 
lowering  of  the  temperature  and  a  corresponding  raising 
of  the  center  of  the  thermal  belt,  while  on  the  windward 
side  the  temperature  is  raised  by  the  constant  inflow  of 
warm  air  on  the  slope,  with  a  consequent  lowering  of  the 
center  of  the  thermal  belt,  although  the  width  or  extent 
of  the  inversion  is  not  necessarily  decreased.  On  the 
southeast  slope  of  Tryon,  for  instance,  under  the  influ¬ 
ence  of  southeast  winds,  while  the  point  of  highest  mini¬ 
mum  lies  relatively  near  the  base  station,  the  thermal 
belt  or  inversion  may  extend  upward  to  No.  4  station, 
and  even  considerably  beyond.  Of  course,  in  such  event 
the  temperature  gradient  from  the  point  of  highest  mini¬ 
mum  upward  is  very  slight  as  compared  with  the  gradient 
between  this  point  and  the  base  station,  and  the  actual 
center  of  the  thermal  belt  does  not  necessarily  coincide 
with  the  point  of  highest  minimum. 

Then  there  is  a  tendency  during  protracted  periods  of 
anticyclonic  weather  with  a  night  or  so  of  absolute  calm 
for  the  belt  to  be  pushed  upward  by  the  failure  of  the 
usual  relief  of  the  unstable  conditions  existing  between 
slope  and  free  air.  The  inflow  of  warmer  air  with  the 
approach  of  a  low-pressure  area  is  first  felt  at  the  more 
elevated  stations,  and  in  extreme  cases  the  temperature 
may  be  rising  at  the  summit  station  and  falling  rapidly 
at  the  levels  below,  because  of  the  reduction  of  wind 
velocity  in  the  valley  by  surface  friction.  The  belt  is 
thus  forced  to  unusual  heights  and  is  higher  with  increas¬ 
ing  length  of  night.  We  would  expect  this  belt  to  be 
lowest  over  a  plain  where  the  radiation  is  confined  to  a 
level  surface  over  which  a  stratum  of  cold  air  is  built 
upward  by  loss  of  heat  from  the  ground,  gradually  affect¬ 
ing  successive  layers  of  air  above,  and  highest  in  a  deep 
and  narrow  valley  where  the  volume  of  air  is  reduced  and 
the  radiation  from  the  opposing  slopes  in  cooling  the  air 
in  contact  with  them  drains  the  small  amount  of  air 
between  the  slopes  of  its  warmth. 


79 


THERMAL  BELTS  AND  FRUIT 


GROWING  IN  NORTH  CAROLINA. 


At  Tryon  we  may  find  the  belt  between  Nos.  2  and  4, 
but  most  frequently  near  and  above  No.  2,  at  an  eleva¬ 
tion  of  about  400  feet  above  No.  1.  The  vertical  tempera¬ 
ture  gradient  at  Tryon  (see  fig.  65)  very  closely  resembles 
that  over  a  plain  as  there  is  no  opposing  slope.  During 
the  occurrence  of  the  mountain  breeze  the  belt  is  forced 
downward  by  the  waterlike  flow  of  cold  air  from  the 
plateau  where  it  has  accumulated.  The  three  slope 
stations  at  Tryon  are  not  directly  in  the  path  of  the 
mountain  breeze,  and  the  small  quantity  of  cold  air 
which  is  forced  over  the  summit  of  Warrior  is  quickly 
warmed  by  mixture  with  the  air  on  the  slope  and  by 
compression  in  its  descent,  and  usually  it  merely  chills 
No.  4  and  possibly  the  slope  a  few  hundred  feet  below, 
with  a  consequent  slight  lowering  of  the  belt.  It  is 
under  these  conditions  that  the  vertical  temperature 
gradient  becomes  strongly  superadiabatic  between  Nos. 
2  and  4  (see  fig.  63).  Under  favorable  conditions, 
previously  described,  the  upper  portion  of  the  thermal 
belt  may  be  so  extended  as  to  include  the  summit  of 
Warrior  above  No.  4,  although  the  highest  minimum  will 
still  be  recorded  at  No.  2. 

The  temperature  of  the  free  air  at  Altapass  is  much 
reduced  by  the  large  area  of  the  radiating  surface  of  the 
surrounding  country.  The  Blue  Ridge  plateau,  nearly 
flush  with  the  surrounding  rim  of  mountains,  is  a  source 
of  much  of  the  unusual  coolness  of  the  slope  stations  as 
compared  with  others  of  the  same  elevation  both  above 
sea  level  and  their  respective  valley  floors.  However, 
since  the  entire  slope  seems  to  be  affected  by  this  unusual 
environment,  as  well  as  the  adjacent  free  air,  the  belt  of 
highest  temperature,  at  least  within  the  limits  of  observa¬ 
tion,  is  found  to  have  practically  the  same  elevation,  as  at 
Globe  and  Gorge,  and  this  condition  is  well  shown  in 
the  following  table,  the  center  of  the  belt  in  each  case 
being  approximately  1,000  feet  above  the  floor: 


Elevation 
of  valley 
floor. 

Average 
elevation 
of  belt  of 
highest 
tempera¬ 
ture. 

Feet. 

1,400 

1,500 

1,625 

Feet. 
2,440 
'  2,480 
i  2, 625 

1  Approximately. 


At  Ellijay  we  have  the  extreme  condition  of  a  narrow 
and  deep  valley  and  reduced  available  free  air,  and  it  is 
not  until  an  elevation  of  1,250  feet  above  the  valley 
floor  and  nearly  3,500  feet  above  sea  level  is  reached  that 
warm  free  air  in  considerable  quantities  is  av  ailable, 
approximated  the  level  of  station  No.  4,  and  because  of 
this  fact  and  the  steadily  decreasing  surface  area,  the 
average  height  of  the  belt  is  placed  somewhat aboveNo.  4. 

At  Sane  River  warm  free  air  is  available  in  considerable 
quantities  above  the  3.000-foot  level  350  feet  above  the 
valley  floor,  and  the  belt  of  highest  temperature  shifts 
between  Nos.  3  and  4,  depending  upon  the  wind  direction. 
No.  3,  which  is  in  a  cove-like  depression  on  the  side  of 
Rocky  Knob,  is  colder  than  points  of  similar  elevation  on 
the  open  slope.  The  700-foot  difference  in  elevation 
between  Nos.  3  and  4  does  not  permit  an  accurate  location 
of  the  belt,  and  although  quite  frequently  the  highest 
temperature  recorded  on  tlie  slope  is  found  at  both 
Nos!  3  and  4,  especially  with  air  movement  from  the 
north,  the  more  rapid  recovery  at  the  higher  station 
after  a  cold  spell  forces  the  belt  to  the  summit  regardless 


of  the  wind  direction.  Thus  the  average  position  is 
placed  slightly  below  No.  4. 

Seasonal  fluctuation  of  the  thermal  belt. — In  an  attempt 
to  determine  whether  or  not  there  is  a  seasonal  fluctua¬ 
tion  in  the  height  of  the  thermal  belt  on  account  of 
difference  in  length  of  nights,  a  comparison  has  been 
made  on  the  Ellijay  and  Tryon  slopes,  having  vertical 
heights  of  1,760  and  1,100  feet,  respectively,  for  which 
figures  are  given  in  Table  20  for  the  spring  and  autumn. 
The  center  of  the  thermal  belt  at  Ellijay  ordinarily 
fluctuates  between  stations  Nos.  4  and  5  and  at  Trvon 
between  Nos.  2  and  3,  as  has  been  shown  already,  so  that 
in  this  comparison  we  need  only  to  use  the  data  for  the 
two  higher  stations  at  Ellijay,  while  at  Tryon  only 
stations  Nos.  2  and  3  are  necessary. 

The  table  gives  the  number  of  nights  during  inversions 
when  each  one  of  these  stations  was  the  warmest  in  its 
group,  for  the  months  of  April,  May,  and  June,  repre¬ 
senting  the  spring,  and  October,  November,  and  De¬ 
cember,  representing  the  autumn.  June  is  used  instead 
of  March  in  the  spring  group  and  December  instead  of 
September  in  the  autumn  group  in  order  to  accentuate 
the  differences  in  the  length  of  nights. 

The  data  are  for  the  four  years  at  Tryon,  1913-1916, 
but  for  onl}r  three  years  at  Ellijay,  as  station  No.  5  there 
was  not  in  operation  until  1914.  A  greater  number  of 
inversions  are  found  on  both  slopes  in  the  spring  than 
in  the  autumn.  In  the  spring  the  highest  minima  are 
observed  at  station  No.  4  at  Ellijay,  78  per  cent  of  the 
total  number  of  nights  of  inversion,  as  compared  with 
22  per  cent  at  No.  5,  while  in  the  autumn  the  percentages 
are  75  and  25,  respectively,  indicating  a  very  slight 
raising  of  the  belt  in  the  autumn.  At  Tryon  in  the 
spring  the  highest  minima  observed  were  82  per  cent  of 
the  time  at  station  No.  2,  as  compared  with  18  per  cent 
at  No.  3,  while  in  the  autumn  the  percentages  were  79 
and  21,  respectively,  the  variation  between  the  two 
seasons  being  the  same  as  at  Ellijay. 

The  above  comparison  has  been  supplemented  by  the 
emplo3rment  of  another  method,  shown  in  Table  20, 
May  and  November  only  being  used.  In  this  method 
the  excesses  in  temperature  at  stations  Nos.  4  and  5  at 
Ellijay  and  at  Nos.  2  and  3  at  Tryon  over  No.  1  in  their 
respective  groups  during  all  nights  of  inversion  in  these 
two  months  for  the  four-year  period  are  included  in 
Table  20,  and  this  comparison  shows  for  Ellijay  per¬ 
centages  of  53  and  47,  respectively,  for  May  and  52  and 
48,  respectively,  for  November,  while  at  Tryon  the  per¬ 
centages  for  May  at  Nos.  2  and  3  are  57  and  43  and  for 
November  54  and  46,  respectively,  confirming  the  results 
obtained  in  the  first  comparison  and  showing  only  a 
slight  excess  at  No.  4  on  the  Ellijay  slope  in  the  spring 
month  of  May  over  that  in  the  fall  month  of  November. 
The  same  may  be  said  for  station  No.  2  at  Iryon  as  com¬ 
pared  with  No.  3.  . 

We  may  conclude  from  these  two  comparisons  that 
there  is  a  tendency,  although  slight,  for  the  thermal  belt 
to  rise  with  the  increase  in  the  length  of  nights.  vV  e  have 
seen  already  that  the  belt  on  the  Ellijay  slope  ordinarily 
assumes  a  high  level  because  of  the  relatn  eL  small  ai  ( a 
near  the  summit  and  the  presence  of  opposing  slopes 
lower  down,  while  at  Tryon  the  point  of  highest  tempei  a- 
ture  is  relatively  low  because  of  the  great  area  m  the 
vicinity  of  the  summit  and  the  lack  ol  opposing  slopes 
at  the  lower  levels.  At  Ellijay,  the  center  of  the  belt  is 
usually  about  1,240  feet  above  the  base  station,  while  at 
Trvon  the  highest  minima  are  found  at  a  point  400  to 
500  feet  above  the  valley  floor,  as  shown  also  in  a  previous 
discussion. 


80 


SUPPLEMENT  NO.  19. 


These  two  belts  are  fairly  representative  of  conditions 
in  mountain  districts  and  they  indicate  the  great  differ¬ 
ences  that  may  exist  in  the  positions  of  the  thermal  belts 
on  slopes  as  modified  by  surrounding  topography. 

Table  20. — Seasonal  fluctuation  of  the  thermal  belt  on  the  two  longest 
slopes,  Ellijay  and  Tryon. 

ELLIJAY  (1914-1916). 


[Number  of  days  with  highest  temperature  at  stations  Nos.  4  and  5.] 


April. 

May. 

June. 

Total. 

Octo¬ 

ber. 

Novem¬ 

ber. 

Decem¬ 

ber. 

Total. 

LO 

id 

TJ4 

id 

»d 

id 

id 

id 

id 

d 

o 

o 

o 

o 

o 

o 

o 

o 

o 

o 

2 

2 

2 

2 

2 

2 

2 

2 

2 

2 

2 

2 

2 

2 

2 

2 

1914 . 

16 

1 

12 

10 

15 

10 

43 

21 

11 

7 

7 

10 

8 

4 

26 

21 

1915 . 

19 

3 

21 

2 

16 

2 

56 

7 

10 

3 

18 

3 

18 

3 

46 

9 

1916 . 

15 

4 

15 

7 

16 

3 

46 

14 

12 

8 

U2 

10 

19 

1 

43 

9 

Total.... 

50 

8 

48 

19 

47 

15 

145 

42 

33 

18 

37 

13 

45 

8 

115 

39 

78 

22 

75 

25 

TRYON  (1913-1916). 

[Number  of  days  with  highest  temperature  at  station  No.  2  or  No.  3.] 


April. 

May. 

June. 

Total. 

Octo¬ 

ber. 

Novem¬ 

ber. 

Decem¬ 

ber. 

Total. 

cd 

CO 

CM 

cd 

=4 

cd 

cd 

cd 

cd 

cd 

cd 

cd 

cd 

cd 

cd 

CO 

o 

o 

o 

o 

o 

d 

o 

o 

o 

o 

o 

o 

o 

o 

o 

o 

2 

2 

2 

2 

2 

2 

2 

2 

2 

2 

2 

2 

2 

2 

2 

2 

1913 . 

12 

7 

18 

6 

22 

9 

52 

22 

18 

4 

18 

5 

14 

4 

50 

13 

1914 . 

15 

6 

21 

5 

22 

2 

58 

13 

17 

11 

21 

9 

7 

2 

45 

22 

1915 . 

21 

5 

22 

2 

17 

4 

60 

11 

12 

2 

18 

2 

16 

2 

46 

6 

1916 . 

21 

2 

25 

4 

26 

2 

72 

8 

24 

4 

22 

3 

13 

4 

59 

11 

Total.... 

69 

20 

86 

17 

87 

17 

242 

54 

71 

21 

79 

19 

50 

12 

200 

52 

Per  cent . 

_ I... 

82 

18 

79 

21 

| 

MONTHLY  TOTALS,  IN  DEGREES  OF  INVERSION  EXCESS,  OF  STATIONS 
NOS.  4  AND  5  OVER  NO.  1  AT  ELLIJAY  AND  OF  STATIONS  NOS.  2  AND 
3  OVER  NO.  1  AT  TRYON. 


Ellijay. 

Tryon. 

May. 

November. 

May. 

November. 

No.  4. 

No.  5. 

No.  4. 

No.  5. 

No.  2. 

No.  3. 

No.  2. 

No.  3. 

1913 . 

186 

158 

248 

??.8 

1914 . 

273 

264 

278 

292 

203 

160 

213 

188 

1915 . 

167 

129 

198 

169 

119 

74 

243 

194 

1916 . 

229 

208 

1 108 

i  85 

205 

136 

177 

134 

Total . 

669 

601 

584 

546 

713 

528 

881 

744 

Per  cent . 

53 

47 

52 

48 

57 

43 

54 

46 

1  Twelve  days  missing. 


TOP  FREEZES  AND  NORMS. 

The  subject  of  inversion  has  now  been  discussed  at 
considerable  length,  and  that  portion  of  the  investiga¬ 
tion  furnishes  most  interesting  data  and  certainly  the 
greatest  complications.  Inversion  conditions  are,  of 
course,  most  important  when  frost  occurs  in  the  lower 
levels,  and  this  situation  has  much  influence  upon  the 
raising  of  fruit.  When  the  temperature  in  the  lower 
levels  does  not  fall  sufficiently  low  for  the  formation  of 
frost,  the  degree  of  inversion  is  of  much  less  consequence. 

There  is  another  phase  of  the  study  of  much  interest — 
the  decrease  in  temperature  with  elevation;  and  we  will 
refer  to  this  subject  under  the  heading  “  Top  freezes 


and  norms.”  The  expression  “Top  freeze”  is  employed 
in  the  mountain  region  to  designate  a  freezing  condition 
in  the  upper  levels  that  may  or  may  not  extend  down 
the  slope  to  the  valley  floor,  but  in  any  case  the  tempera¬ 
ture  is  lowest  at  the  summit.  Top  freezes  are  included 
in  norms,  but  there  are  many  cases  that  we  shall  have  to 
consider  where  the  temperatures  are  not  below  the  freez¬ 
ing  point,  although  still  with  approximately  the  same 
decrease  with  elevation.  The  term  “norm”  has  been 
used  in  previous  chapters  of  this  publication  and  it  seems 
to  be  acceptable,  as  the  word  indicates  the  return  to 
what  may  be  considered  approximately  normal  or  natural 
conditions. 

The  subject  was  touched  upon  on  previous  pages  in 
connection  with  the  study  oi  average  minimum  tem¬ 
perature,  and  it  was  shown  that  during  the  selected 
norm  periods  (fig.  49)  the  minimum  temperature  de¬ 
creased  more  or  less  regularly  from  the  lowest  to  the 
highest  levels  and  that  the  rate,  of  decrease  between 
the  lowest  and  highest  stations  employed  in  the  research, 
Tryon  No.  1  ana  Highlands  No.  5,  was  1.2°  for  each 
300  feet  of  ascent,  as  compared  with  a  normal  decrease 
of  1°  for  each  300  feet  in  free  air. 

An  examination  of  the  observations  on  the  long  slopes 
during  the  research  shows  marked  instances  of  norms, 
as  well  as  of  inversions,  during  the  winter  months,  but 
they  are  relatively  less  frequent  during  the  other  seasons 
of  the  year.  Naturally  norms  on  short  slopes  are  of 
little  consequence.  The  forms  containing  the  observa¬ 
tions  at  Ellijay  during  certain  selected  months,  January, 
1916,  February,  1915,  and  March,  1916,  Tables  11,  12, 
and  21,  respectively,  embrace  fairly  representative  con¬ 
ditions  for  these  particular  months.  Ellijay  is  the 
longest  slope  used  in  the  study,  1,760  feet,  and  the 
observations  on  that  slope  bring  out  the  features  of 
norms  strongly,  just  as  they  do  of  inversions.  Of  course, 
there  is  not  the  same  range  in  norms  that  there  is 
in  inversions,  the  decrease  seldom  reaching  10°,  while 
inversions  may  often  exceed  20°,  as  shown  in  Table  7. 
Norms  ordinarily  occur  during  cloudy  weather,  with 
rather  strong  winds  between  southwest  and  north,  such 
as  ordinarily  usher  in  cold  weather.  If  the  weather  is 
clear,  there  is  a  tendency  to  inversion,  although,  if 
the  wind  is  sufficiently  brisk,  this  tendency  is  neutral¬ 
ized.  In  Table  21,  March,  1916,  at  Ellijay  there  are 
18  instances  of  norms,  as  shown  by  a  comparison  of 
the  summit  with  the  base  station,  but  in  no  case  is  there 
a  greater  range  than  11°.  In  January  of  the  same  year 
(Table  11)  there  are  19  instances  of  norms,  with  the 
greatest  range  reaching  10°,  and  in  February,  1915 
(Table  12),  only  11  instances,  the  greatest  range  being 
as  small  as  7°.  These  three  months  are  fairly  typical 
of  conditions  in  the  colder  months  of  the  year.  In  the 
above  figures  dates  having  norms  as  small  as  1°  even  are 
included,  although  this  rate,  considering  the  differences 
in  elevation,  is  well-nigh  inappreciable. 

It  may  be  said  that  a  norm  is  characteristic  of  a 
change  to  colder  weather  when  the  wind  velocity  is 
sufficiently  strong  to  prevent  inversion,  the  amount  of 
difference  in  temperature  between  tbe  summit  and 
base  stations  depending  almost  wholly  on  the  differ¬ 
ences  in  topography.  Norms  do  not  occur  always  in 
cloudy  weather,  as  cloudiness  is  sometimes  character¬ 
istic  of  the  Intermediate  or  Cyclonic  Type  of  inversion 
when  there  is  an  overrunning  of  warmer  air  either  im¬ 
mediately  after  the  passage  of  the  anticyclone  or  directly 
before  the  arrival  of  the  low-pressure  area. 


THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 


Table  21.— Monthly  record  of  minimum  temperatures,  daily  precipita¬ 
tion,  wind  direction  and  force,  and  state  of  weather,  also  differences 
between  readings  at  base  station  and  those  on  slope,  March ,  1916  Elliiav 
selected  month  showing  norms .  ’  J 


[The  differences  between  readings  at  the  base  and  the  respective  slope  stations  may  be 

seen  by  inspection.] 


Date. 

Temperature. 

Precipitation  at  6 
p.  m.  (inches). 

Wind. 

State  of  weather. 

Station  1,  base. 

£ 

d2 
O  CO 

Vs 

C3 

CO 

Station  3,  N., 
620.1 

Station  4,  N., 
1,240.1 

Station  5, 
1,760.1 

Sunrise. 

Sunset. 

Previous 

night. 

Day. 

Dir. 

Force. 

Dir. 

Force. 

1... 

21 

23 

22 

23 

23 

0.00 

sw. 

Mod... 

SW. 

Mod... 

Cloudy.. 

Cloudy. 

2. . , 

32 

31 

32 

31 

29 

0. 36 

w. 

...do... 

w. 

Brisk  . 

. .  .do . 

3.. . 

26 

22 

20 

18 

19 

0.00 

nw. 

Brisk . 

nw. 

...do... 

..  .do . 

Cloudy. 

4. . . 

10 

11 

10 

9 

7 

0. 01 

nw. 

Mod... 

nw. 

Mod... 

. .  .do . 

5. . . 

25 

31 

31 

32 

28 

0.  00 

w. 

...do... 

w. 

.  -do... 

Clear. . . . 

Do. 

6.. . 

36 

41 

41 

45 

41 

0. 00 

sw. 

Brisk . 

sw. 

Brisk . 

Cloudy.. 

Cloudy. 

7. . . 

46 

44 

44 

45 

39 

0.42 

w. 

...do... 

nw. 

. .  .do.. . 

. .  .do _ 

Pt.  cldv. 

8.. . 

21 

19 

16 

13 

13 

0.00 

nw. 

...do... 

nw. 

.  ..do... 

Pt.cldv. 

Cloudy. 

9 _ 

11 

13 

11 

8 

7 

T. 

w. 

...do... 

w. 

Mod... 

Cloudy.. 

Clear. 

10.. . 

22 

24 

26 

26 

21 

0.00 

w. 

...do... 

w. 

Brisk . 

Clear. . . . 

Cloudy. 

11.. . 

23 

25 

24 

22 

18 

0.00 

w. 

.  ..do... 

w. 

Mod... 

. .  .do . 

Clear. 

12.. . 

19 

21 

22 

23 

18 

0.00 

w. 

Mod... 

w. 

.  ..do... 

. .  .do . 

Do. 

13.. . 

29 

35 

37 

41 

33 

0.00 

w. 

.  ..do... 

w. 

Brisk . 

. .  .do . 

Do. 

14.. . 

39 

46 

51 

52 

49 

0.00 

w. 

Brisk . 

w. 

.  ..do... 

...do . 

Do. 

15... 

30 

28 

25 

23 

23 

0. 25 

w. 

Gale. . 

nw. 

.  ..do... 

Cloudy.. 

Cloudy. 

16.. . 

10 

12 

9 

6 

4 

0.00 

nw. 

Brisk . 

nw. 

Mod... 

. .  .do . 

Clear. 

17... 

17 

19 

20 

19 

16 

0.00 

nw. 

Mod... 

nw. 

.  ..do... 

Clear. . . . 

Do. 

18... 

25 

28 

30 

37 

32 

0.00 

w. 

Brisk . 

w. 

Brisk . 

. .  .do . 

Do. 

19... 

48 

45 

43 

43 

37 

0.00 

w. 

.  ..do... 

w. 

...do... 

..  .do . 

Do. 

20.. . 

31 

33 

30 

35 

33 

0.00 

nw. 

Mod... 

nw. 

.  ..do... 

. .  .do . 

Do. 

21.. . 

41 

42 

39 

40 

3S 

0. 26 

nw. 

Brisk . 

nw. 

Mod... 

Cloud  v.. 

Pt.  cldv. 

22.. . 

54 

59 

55 

55 

50 

0.00 

nw. 

.  ..do... 

w. 

High. . 

. .  .do . 

Cloudy. 

23.. . 

26 

28 

27 

28 

29 

0.00 

w. 

.  ..do... 

w. 

Brisk . 

Clear. . . . 

Clear. 

24... 

39 

46 

44 

46 

42 

0.00 

w. 

.  ..do... 

w. 

Mod... 

. . .do . 

Do. 

25.. . 

47 

54 

52 

54 

49 

0.00 

s. 

Mod... 

sw. 

.  ..do... 

Pt.cldy. 

Do 

26... 

57 

58 

56 

56 

51 

0.00 

sw. 

.  ..do... 

s. 

Brisk . 

Cloudy.. 

Cloudv. 

27.. . 

40 

42 

37 

44 

42 

1.17 

w. 

Brisk . 

w. 

Mod... 

. . .do . 

Do. 

28... 

36 

35 

34 

33 

29 

0.02 

nw. 

.  ..do... 

nw. 

Brisk  . 

...do . 

Do. 

29... 

35 

33 

31 

29 

27 

0.00 

n. 

Mod... 

n. 

Mod... 

. . .do . 

Pt.cldy. 

30.. . 

29 

30 

32 

35 

32 

0.00 

ne. 

...do... 

ne. 

. .  .do... 

Clear. . . . 

Clear. 

31... 

31 

35 

36 

40 

40 

0.00 

w. 

...do... 

w. 

Brisk . 

..  .do . 

Do. 

Sum. 

956 

1,013 

987 

1,013 

915 

2.49 

Mean 

30.8 

32.7 

31.8 

32.7 

29.5 

1  Direction  of  slope  and  elevation  of  station  above  base  station. 
Mod.=moderate;  Lt.=light;  Pt.=partly. 


Norms  on  selected  long  slopes  having  a  vertical  height  of 
1,000  feet  or  more. — Table  22  presents  norm  data  for  the 
six  long  slopes,  Altapass,  Cane  River,  Ellijay,  Globe, 
Gorge,  and  Tryon,  including  comparisons  of  frequency 
and  range  of  norms,  after  the  plan  of  the  discussion  of 
inversions  on  the  basis  of  5°  or  more  range  in  tempera¬ 
ture  (Table  13),  but  Table  22  has  not  been  supplemented 
by  additional  tables  in  order  to  show  greater  norms,  be¬ 
cause  the  range  between  base  and  summit  seldom  equals 
10°.  In  fact,  the  record  norms  for  the  four-year  period, 
as  shown  in  the  summary  of  the  table,  are  as  follows: 
Altapass  8°;  Cane  River,  10°;  Ellijay,  11°;  Globe,  8°; 
Gorge,  8°;  and  Tryon,  10°.  Ellijay,  with  its  vertical 
height  of  1,760  feet,  is  the  only  slope  on  which  a  norm 
greater  than  10°  was  observed  in  the  entire  four  years. 
The  largest  there  was  11°,  December  9,  1916,  as  shown 
in  Figure  67,  and  one  of  10°  was  registered  on  six  dates. 

That  figure  has  been  prepared  to  show  graphically  the 
monthly  variation  in  the  frequency  of  norms,  as  well  as 
the  average  and  extreme  amounts  for  the  six  long  slopes, 
and  is  comparable  with  the  graph  representing  inver¬ 
sions  (fig.  52). 

In  including  Altapass  in  the  study  of  the  frequency  of 
inversions  in  connection  with  Table  13,  there  is  a  certain 
complication  in  that  there  was  no  valley-floor  station 


available  on  that  slope  during  the  period  of  the  research 
and  the  temperature  readings  do  not  therefore  indicate 
the  range  of  inversion  that  is  shown  by  the  groups  having 
valley  floor  stations.  However,  it  would  seem  that  the 
employment  of  the  Altapass  slope  in  Table  22  in  connec¬ 
tion  with  the  frequency  and  range  of  norms  would  be 
free  from  the  complications  apparent  in  the  study  of 

Inversions,  and  this  is  found  to  be  true,  as  the  degree 
of  norm  depends  less  upon  the  topography  than  upon 
the  differences  in  elevation  between  the  vai’ious  points 
under  consideration.  However,  Ellijay,  the  longest 
slope,  has  by  no  means  the  largest  number  of  inversions, 
but  ranks  in  the  entire  period  fourth  of  the  six  long 
slopes. 

In  Table  22  Altapass  is  shown  to  have  the  largest 
number  of  norms  of  5°  or  more,  284;  Tryon,  with  264; 
Cane  River,  195;  Ellijay,  167;  Gorge,  119;  and  Globe, 
69.  Altapass,  with  the  greatest  number,  and  Globe, 
with  the  smallest  number,  each  having  the  same  vertical 
height  between  their  base  and  summit  stations,  1,000 
feet.  The  largest  norm  observed  on  either  slope  is  8°, 
while  the  average  is  6°  and  5°,  respectively.  Altapass, 
situated  on  the  summit  of  the  main  chain  of  the  Blue 
Ridge,  has  no  protection  to  the  north  and  west  in  the 
vicinity,  while  Globe  has  the  protection  to  the  northwest 
of  Grandfather  Mountain,  the  most  massive  mountain 
in  the  entire  North  Carolina  region.  The  question  of 
surface  area  in  the  immediate  vicinity  has  doubtless  an 
important  bearing  in  the  matter  of  norms.  Altapass,  on 
whose  slope  the  largest  number  of  norms  occurs,  not 
only  has  no  protection  to  the  north  and  west,  but  also 
has  great  surface  area  in  the  vicinity  of  the  summit;  and 
Tryon,  ranking  second  on  the  list  of  the  number  of  norms 
also  has  great  surface  area  near  the  summit,  while  Cane 
River,  Gorge,  and  Ellijay  have  comparatively  little  area 
at  the  summit.  Globe,  however,  which  ranks  lowest, 
although  having  considerable  area  in  the  direction  of 
Grandfather  Mountain,  at  the  same  time  has  the  protec¬ 
tion  of  that  vast  peak,  and  the  winds  from  the  northwest 
coming  from  it  are  always  descending  and  being  warmed 
mechanically  on  their  arrival  at  the  base  station.  Doubt¬ 
less  the  presence  of  protecting  ranges  in  the  direction 
from  which  cold  waves  come  is  a  factor. 

Furthermore,  at  Altapass  the  range  of  temperature 
considered  is  between  the  summit  and  No.  1,  and  the 
fact  that  the  latter  station  happens  to  be  on  a  slope 
may  be  an  additional  reason  for  the  large  number  of 
norms,  and  as  Tryon  No.  1  is  located  on  an  ideal  valley 
floor  the  mountain  breeze  frequently  occurs  at  night, 
often  being  intensified  by  the  movement  of  the  air  from 
the  plateau  above,  and  on  that  account  the  readings  of 
the  base  station  are  at  times  much  higher  than  those  at 
the  summit.  Some  of  the  norms  included  in  Table  22, 
especially  for  Altapass  and  Tryon,  really  occurred  on 
nights  of  inversion— that  is,  when  the  temperature  was 
higher  on  the  intermediate  slope — and  this  fact  should 
partly  account  for  the  large  number  credited  to  those 
two  slopes.  That  Altapass  and  Tryon  have  a  large  num¬ 
ber  of  norms  is  important,  and  the  fact  that  Ellijay  with 
its  longer  slope  has  a  much  smaller  number  is  equally 
important,  especially  when  it  is  considered  that  all 
norms  of  5°  are  included  in  this  comparison. 


S2 


SUPPLEMENT  NO.  19. 


Table  22. — Total  monthly  and  annual  number  of  norms  of  5°  or  more  on  si.r  long  slopes  (1913-1916,  inclusive). 


Stations. 

Jan. 

Feb. 

Mar. 

Apr. 

May. 

June. 

July. 

Aug. 

Sept. 

Oct. 

Nov. 

Dec. 

Annual. 

a 

b  1  c 

d 

a 

b 

c 

d 

a 

b 

c 

d 

a 

b 

c 

d 

a 

b 

c 

d 

a 

b 

c 

d 

a 

b 

c 

d 

a 

b 

c 

d 

a 

b 

c 

d 

a 

b 

c 

d 

a 

b 

c 

d 

a 

b 

c 

d 

a 

b 

c 

d 

1913. 

Altanass . 

1  4 

■  r. 

>n 

ifi 

16 

in 

19 

■fi 

6 

fi 

0 

7 

4 

fi 

713 

5 

5 

5 

5 

1 

0 

<i 

2 

6 

fi 

10 

14 

11 

6 

815 

6 

5 

7 

24 

13 

fi 

7 

10 

82 

6  10 

Sept.  14. 

Cane'  River . 

i  7 

1  M 

ui 

ifi 

>7 

ui 

9 

(i 

8 

27 

3 

(i 

7 

24 

2 

5 

510 

0 

0 

. . 

.  . 

1 

5 

5 

21 

2 

6 

t) 

10 

2 

fi 

6  21 

2 

6 

f) 

10 

2 

0 

7 

S 

48 

fi 

8 

Apr.  27. 

Ellijay . 

1  3 

'6 

‘5 

>6 

1  3  lfi 

4 

6 

7 

10 

2 

5 

5  24 

0 

0 

0 

0 

0 

0 

1 

6 

ti 

21 

2 

fi 

6 

20 

2 

0 

fi 

10 

4 

6 

9 

31 

26 

fi 

9 

Dec.  31. 

3 

(i 

4 

3 

5 

5 

7 

3 

5 

ti 

10 

2 

6 

fi 

1 

5  24 

0 

0 

0  0 

0 

0 

0 

0 

0 

(1 

1 

0 

(i 

9 

1 

5 

5 

8 

14 

0 

Nov.  9. 

Gorge . 

3 

7 

7 

3 

i 

5 

5 

7 

2 

f, 

0 

27 

1 

5 

5 

5 

0 

0 

0 

0 

0 

0 

1 

5 

513 

1 

5 

5 

17 

2 

5 

5 

24 

3 

0 

7 

9 

3 

5 

5 

1 

17 

5 

7 

Jan.  3. 

Tryon . 

3 

5 

5 

28 

ii 

7 

8 

5 

4 

7 

9 

22 

9 

9 

7 

5 

4 

7 

7 

7 

6 

7 

9  13 

(i 

5 

fi 

i9 

5 

0 

6  21 

2 

0 

6 

14 

8 

8 

1131 

4 

8 

9 

24 

6 

0 

0 

27 

68 

6 

10 

Oct.  31 

Total,  col- 

uma  (a) . 

Average,  col- 

23 

6 

7 

3 

42 

6 

8 

5 

25 

0 

9 

22 

34 

6 

8  27 

16 

(i 

7 

7 

12 

6 

9  13 

11 

5 

6 

19 

8 

5 

6  21 

12 

6 

10 

14 

25 

6 

11  31 

18 

6 

9 

24 

29 

6 

9 

31 

255 

fi 

in 

Oct.  31. 

Greatest,  col- 

lima  (c) . 

1914. 

11 

5 

0  22 

0 

0 

7 

1 

8 

0 

fi 

2 

7 

7 

27 

7 

5 

0 

5 

6 

17 

6 

0 

6 

IS 

1 

5 

5  30 

1 

5 

5 

13 

7 

5 

6  10 

11 

6 

8 

10 

15 

0 

7 

30 

87 

5 

8 

Nov.  10. 

Cane*  River . 

12 

6 

10  17 

8 

7 

9 

7 

17 

Mi 

9 

fi 

8 

2 

3 

6 

7 

5 

3 

6 

716 

1 

5 

5 

7 

1 

5 

5 

4 

3 

0 

0 

13 

6 

6 

9  27 

3 

6 

0 

17 

9 

6 

8 

31 

65 

b 

10 

Jan.  17. 

Ellijay . 

6 

6 

7  31 

6 

fi 

7  lfi 

7 

8 

io 

9 

4 

7 

9 

2 

2 

fi 

7 

9 

1 

5 

5 

IS 

0 

0 

0 

0 

2 

fi 

ti 

10 

3 

6 

7 

3 

4 

(i 

7 

20 

0 

0 

9 

10 

41 

0 

10 

Mar.  9. 

ftlnhft . 

1 

5 

0 

4 

3 

5 

5 

(i 

3 

5 

2 

1 

9 

0 

0 

0 

0 

0 

0 

0 

0 

ii 

0 

... 

0 

0 

2 

5 

5 

20 

'2 

6 

fi 

13 

12 

5 

0 

Dec.  13. 

Gorge . 

3 

5 

5  31 

5 

f, 

6 

0 

fi 

fi 

7 

20 

3 

<) 

7 

9 

0 

0 

4 

5 

ti  19 

0 

0 

0 

0 

.. 

4 

5 

6 

13 

4 

5 

5 

24 

5 

6 

8 

16 

5 

0 

8 

26 

39 

6 

8 

Dec.  26. 

Tryon . 

12 

6 

9 

4 

(3 

6 

7  15 

8 

fi 

823 

3 

0 

7  21 

0 

0 

-- 

4 

fi 

7 

30 

5 

6 

8,25 

4 

6 

6  22 

4 

5 

Ii 

13 

3 

< 

9,12 

4 

6 

6 

20 

15 

0 

7 

14 

68 

0 

9 

Oct.  12. 

Total,  col- 

uma  (a) . 

Average,  c  o  1- 
umn  (b) . 

45 

6 

1017 

34 

6 

9 

7 

39 

6 

10 

9 

27 

6 

9 

2 

12 

6 

7 

9 

19 

5 

7 

1612 

6 

8 

25 

6 

fi 

6 

22 

14 

5 

6 

13 

23 

6 

9 

12 

29 

6 

8 

16 

52 

0 

9 

10 

312 

6 

10 

Mar.  9. 

Greatest,  col- 

umn  (c) . 

1915. 

7 

5 

7  15 

1 

5 

5 

13 

6 

6 

7 

2 

8 

6 

7 

12 

0 

6 

6 

17 

4 

5 

9 

3 

5 

fi 

3 

2 

5 

5 

9 

0 

0 

1 

5 

5 

24 

4 

0 

7 

22 

8 

5 

0 

30 

50 

5 

7 

Cane*  River . 

9 

fi 

8  23 

f) 

6 

8 

7 

9 

7 

7 

1 

2 

« 

7 

1 

2 

fi 

6 

7 

1 

0 

6  25 

2 

6 

6 

10 

2 

0 

6 

13 

1 

5 

5 

30 

0 

0 

5 

6 

7 

15 

5 

6 

7 

13 

44 

6 

8 

Feb.  7. 

Ellijay . 

0 

7 

9  28 

6 

7 

7 

8 

8 

7 

8 

8 

1 

7 

7 

3 

2 

5 

5 

7 

4 

5 

5 

29 

0 

0 

1 

5 

5 

28 

2 

.5 

5 

30 

2 

fi 

6 

7 

7 

7 10 

29 

5 

8 

10 

IS 

44 

6 

10 

Nov.  29. 

Globe . 

2 

fi 

6  22 

3 

5 

6  25 

2 

6 

0  23 

0 

0 

0 

0 

1 

5 

5 

21 

0 

0 

0 

0 

1 

5 

5 

1 

1 

5 

5 

8 

2 

5 

5 

29 

1 

5 

5 

14 

13 

5 

fi 

Mar.  23. 

2 

5 

0  27 

7 

5 

7,25 

5 

5 

0  17 

0 

0 

5 

5 

5 

31 

2 

5 

5 

4 

1 

5 

5 

1 

5 

5 

28 

2 

5 

5 

30 

2 

0 

18 

0 

0 

0 

0 

27 

5 

Feb.  25. 

Tryon . 

5 

5 

7 

13 

fi 

6 

7,16 

11 

6 

8  21 

1 

6 

6 

'4 

6 

7 

9 

30 

0 

0 

1 

6 

6 

13 

2 

ti 

6 

0 

1 

5 

5 

5 

6 

7 

9 

9 

5 

7 

8 

27 

10 

6 

8 

13 

54 

6 

9 

Oct.  9. 

Total,  col- 

Average,  col- 

31 

6 

9,28 

29 

0 

8 

7 

41 

6 

8 

8 

12 

6 

7 

3 

21 

0 

9 

30 

12 

5 

6 

25 

7 

6 

6 

13 

8 

5 

6 

13 

7 

5 

5 

30 

12 

6 

9 

9 

23 

6 

10 

29 

29 

6 

10 

18 

232 

6 

10 

Nov.  29. 

Greato't,  col- 

umn  (c) . 

1916. 

Altapass . 

fi 

6 

6,23 

9 

5 

0 

21 

10 

7 

6 

23 

5 

6 

7 

10 

4 

5 

6 

5 

7 

5 

7 

4 

1 

0 

6 

4 

5 

6 

7 

14 

5 

5 

r> 

lfi 

2 

5 

5 

22 

7 

6 

7 

26 

4 

6 

0 

1 

65 

6 

7 

Nov.  2fi. 

Cane  River . 

5 

5 

617 

5 

fi 

7 

14 

8 

6 

8 

8 

6 

fi 

9 

22 

2 

7 

8 

17 

2 

(i 

6 

7 

2 

0 

5 

30 

0 

0 

2 

6 

7 

13 

3 

5 

5 

21 

1 

9 

9 

24 

2 

6 

6 

lfi 

38 

fi 

9 

Apr.  22. 

Ellijay . 

9 

7 

10  17 

8 

7 

11  27 

9 

7 

8 

8 

4 

7 

8 

9 

1 

(i 

6 

22 

2 

8 

10 

7 

9 

7 

10 

11 

1 

6 

6 

3 

2 

6 

8 

29 

4 

6 

7 

n 

3 

9 

10 

24 

4 

8 

9 

22 

56 

7 

11 

Feb.  27. 

Globe . 

3 

5 

5 

7 

4 

fi 

7 

211 

3 

fi 

8 

lfi 

5 

fi 

8 

22 

0 

0 

0 

0 

0 

0 

3 

fi 

7 

1 

2 

fi 

0 

29 

2 

6 

6 

18 

3 

7 

8 

24 

5 

8 

11 

22 

30 

fi 

8 

Dec.  22. 

Gorge . 

fi 

(i 

6 

13 

6 

fi 

7  27 

5 

.5 

6  27 

3 

5 

5 

9 

2 

5 

5 

22 

1 

5 

5 

in 

1 

5 

5 

io 

3 

5 

fi 

18 

3 

fi 

8 

2 

2 

6 

7 

18 

3 

5 

5 

25 

1 

6 

ti 

9 

36 

5 

8 

Sept.  2. 

Tryon . 

6 

6 

8 

3 

10 

6 

628 

fi 

6 

7 

4 

4 

5 

6 

22 

1 

5 

5 

22 

1 

9 

9 

17 

5 

0 

9 

4 

12 

6 

9 

2 

7 

7 

9 

R 

7 

6 

10  21 

8 

6 

10 

25 

7 

7 

9 

1 

74 

6 

10 

Oct.  21. 

Total,  col- 

umn  (a) . 

Average,  col¬ 
umn  (b) . 

35 

6 

10 

17 

42 

6 

11 

27 

41 

6 

9  10 

27 

6 

9 

22 

10 

6 

8 

17 

13 

7 

10 

7 

18 

6 

10 

11 

24 

6 

9 

2 

21 

6 

9 

fi 

20 

6 

10 

21 

25 

7 

11 

16 

23 

7 

12 

29 

299 

6 

12 

Dec.  29. 

Greatest,  co  1- 

umn  (c) . 

1 9X3— 191 H. 

Altapass . 

Cane  River . 

Ellijay . 

Globe . 

Gorge . 

Tryon . 

Total,  column  (a). .. 
Average,  column  (b) 
Greatest,  column  (c) 


Jan. 


131 


in 


Feb. 


147 


fi  7 
6  9 
611 

5  7 

6  7 
6  S 


fi  11 


Mar. 


Apr. 


a  b 


30  6 

31  fi 
27  7 
11  fi 
IS,  fi 
29  fi 


14fi  fi 


10 


100 


May. 


8  23 

9  10 


59 


June. 


5  7 

6  7 
610 
5'  5 
5!  6 
7'  9 


July. 


■Vi 


6  10 


48 


6 
6 
710 
0  - 
5  5 
fi  9 


fi  10 


Aug. 


4fi 


Sept. 


a  ,b 


12 

8 

7 

3 

10 


14  6 


54  6 


10 


Oct. 


80 


b  I  c 


5!  8 
fi|  9 
«,  7 
fi;  6 
fi  7 
7  11 


fill 


Nov. 


95 


Dec. 


718 
7  9 
7i°; 
fi!  8 1 
fil  8i 

7|10| 


710  133 


7  10 
fi  11 


11 


Four-vear  annual. 


284 

195 

167 

fi9 

119 

2R4 


1,098 


Nov.  lfi. 
Jan.  17. 
Feb.  27. 
Dec.  22. 
Dec.  2fi. 
Oct.  31. 


Feb.  27, 191fi. 


1  Values  interpolated. 

(a)  Number  of  nights  during  which  a  difference  of  5°  or  more  occurred  between  base  and  summit  stations. 

(b)  Average  (degrees)  differences  between  base  and  summit  stations. 

(c)  Amount  (degrees)  of  greatest  norm. 

(d)  Date  of  greatest  norm. 


-3 


THERMAL  BELTS  AND  FRUIT 


GROWING  IN  NORTH  CAROLINA. 


Naturally  the  largest  number  of  norms  occurs  in  the 
coldest  and  most  stormy  season  of  the  year  (Fig.  67)  or 
when  the  vapor  pressure  is  least,  February  having  147 
March  14G,  January  134,  and  December  133.  July  and 


Fig.  67. — Monthly  frequency  and  average  and  extreme  degrees  of  norm  on  six  long 

slopes. 

August  have  the  least  number,  48  and  46,  respectively, 
doubtless  because  of  the  lack  of  storm  movement  and 
high  humidity.  The  largest  number,  312,  occurred  in 
1914,  while  the  smallest  number  was  232,  in  1915. 


While  periods  of  inversion  of  large  amounts  often 
last  a  week  and  sometimes  even  two  weeks,  as  shown  by 
Tables  5  and  7,  which  give  the  daily  minimum  tempera¬ 
tures  and  variations  for  Ellijay  for  May  and  November, 
respectively,  1914,  norm  periods  exceeding  5°  seldom 
last  more  than  a  few  days  at  a  time,  even  in  the  winter 
season;  but  periods  of  small  norms  mav  continue  for 
prolonged  periods,  as  in  January,  1916  (Table  11).  Gen¬ 
erally  speaking,  the  frequency  of  inversions  is  much 
greater  than  that  of  norms.  Comparing  Table  13,  giv¬ 
ing  the  number  of  inversions  of  5°  or  more  for  the  entire 
period  in  North  Carolina  on  the  six  slopes  having  a 
length  of  1,000  feet  or  more,  with  the  number  of  norms 
of  the  same  degree  in  Table  22  we  find  that  the  inversions 
total  3,316,  as  compared  with  the  total  norms,  1098.  In 
other  words,  inversions  occur  almost  three  times  as  fre¬ 
quently  as  norms.  This  is  in  itself  most  important. 

Of  the  individual  slopes,  Altapass  is  the  only  one  dur¬ 
ing  the  research  period  which  has  a  larger  number  of 
norms  than  inversions,  284  as  compared  with  173,  but 
this  fact  is  only  apparent  and  not  real,  as  the  number  of 
inversions  on  the  Altapass  slope  is  not  indicated  in  any 
degree  in  Table  13  because  of  the  absence  of  a  base  station 
there. 

Of  the  other  slopes,  Trvon  has  barely  twice  as  many 
inversions  as  norms,  the  percentage  there  being  smaller 
than  on  the  remaining  slopes  because  of  the  great  mass  at 
the  summit  at  Tryon  and  the  mountain  breeze  at  the 
base  station  at  night,  to  both  of  which  conditions  refer¬ 
ence  has  been  made  before. 

On  the  other  hand,  Gorge  has  during  the  period  705 
inversions,  as  compared  with  119  norms,  and  Globe  549 
inversions,  as  compared  with  69  norms,  the  preponderance 
of  inversions  at  the  latter  station  being  the  greatest  of 
all. 

Individual  instances  of  norms  may  be  noted  by  a 
study  of  the  various  thermograph  traces  (figs.  59,  60,  68, 
and  69).  Moreover,  Figure  68  illustrates  the  top  freeze 
or  norm  condition  during  the  selected  period  in  De¬ 
cember,  1916,  for  Ellijay,  as  well  as  the  inversion,  and 
shows  the  vertical  distribution  of  temperature  during  a 
period  of  active  weather  in  December  by  means  of  iso- 
pleths  in  the  upper  portion  of  the  graph  and  by  the 
superimposed  traces  of  the  summit  and  base  stations  in 
the  lower  part  of  the  graph. 

Isopleths  showing  progressive  distribution  of  temperature 
at  Ellijay  during  a  December  period. — The  isopleth  in 


Fig.  68.— Isopleths  and  thermograph  traces,  selected  period,  December,  1916,  ElUjay. 


84 


SUPPLEMENT  NO.  10. 


Figure  68  shows  the  distribution  of  temperature  on  the 
1,760-foot  slope  at  Ellijay  during  a  period  of  the  more 
active  weather  conditions,  which  are  typical  of  the 
colder  season  of  the  year,  from  noon,  December  8,  to 
noon,  December  10,  i916.  The  upper  portion  of  the 
graph  gives  the  temperature  distribution  during  a  warm, 
cloudy,  and  rainy  period,  showing  a  small  decrease  in 
temperature  with  elevation  followed  by  a  sharp  cold 
wave  beginning  at  about  3 :30  a.  m.  of  the  9th.  The 
high  northerly  winds  over  this  region  bring  cold  air 
to  the  summits  faster  than  they  can  drive  the  warm 
air  out  of  the  valleys  below,  so  that  the  vertical  tem¬ 
perature  gradient  is  much  increased  and  not  infrequently 
superadiabatic  during  a  cold  wave.  This  is  well  shown 
during  the  morning  of  the  9th  and  to  a  lessening  degree 
during  the  remainder  of  the  daylight  hours,  the  tem¬ 
perature  at  8  a.  m.  of  the  9th  being  36°  at  No.  1  and 
25°  at  No.  5.  The  rate  of  decrease  in  temperature 
between  base  and  summit  at  this  hour,  11°  for  1,760 
feet,  or  practically  2°  for  each  300  feet,  is  twice  the 
average  rate  in  free  air. 


ALTA  PA-53  *  /  ^  3 - ELLIJAY  «►  /  «/-  3 - 


Fig.  69. — Thermograph  traces,  March  2-4, 1916,  stations  Nos.  1  and  5,  Ellijay. 

But  with  clear  weather  and  diminishing  wind  velocity, 
a  slow  recovery  in  temperature  begins  at  the  summit 
station  at  about  9  p.  m.  of  the  9th,  with  the  center  of 
high  pressure  moving  northeastward. 

The  lower  portion  of  the  graph  contains  thermograph 
traces  for  Nos.  1  and  5  during  the  same  period  from 
noon  December  8  to  noon  December  10,  1916,  and  illus¬ 
trates  graphically  the  norm  conditions  on  the  9th, 
gradually  changing  to  those  of  inversion  during  the 
succeeding  night  and  reaching  the  greatest  develop¬ 
ment  by  about  8  a.  m.  of  the  10th. 

HOUR-DEGREES  OF  FROST. 

In  fruit  growing  the  degree  to  which  the  temperature 
falls  on  a  critical  night  is  important,  but  the  duration  of 
the  damaging  temperature  must  be  given  equal  consider¬ 
ation.  The  injury  to  fruit  on  two  different  nights  when 
the  temperature  falls  to  30°,  for  instance,  will  vary 
greatly,  provided  there  is  a  great  difference  in  the  length 
of  time  the  temperature  remains  below  32°.  In  one  case 
the  temperature  may  rise  almost  immediately  after  the 
low  point  is  reached,  and  freezing  temperature  may  last 
only  an  hour  or  so,  while  in  the  other  case  the  recovery 


from  the  low  point  may  be  very  slow,  with  freezing  tem¬ 
perature  continuing  for  several  hours. 

In  order  to  represent  the  volume  of  freezing  tempera¬ 
ture,  so  to  speak,  a  numerical  value,  called  "hour-degrees 
of  frost,”  has  been  employed  in  this  study.  This  idea  is 
analogous,  broadly  speaking,  to  the  "kilowatt-hour” 
magnitude  used  in  electrical  measurements.  In  other 
words,  the  quantity  of  hour-degrees  of  frost  is  the  product 
of  the  number  of  hours  and  degrees  below  32°,  and  this 
has  been  found  through  the  use  of  a  planimeter  by  measur¬ 
ing  the  area  on  the  thermograph  trace  sheets  between 
the  temperature  curves  and  the  32°  line.  The  symbol, 
HF°,  will  be  employed  here  in  designating^ the  volume. 

In  the  discussion  of  the  data  of  Hour-Degrees  of  Frost 
reference  will  be  made  as  far  as  practicable  to  the  amount 
and  extent  of  damage  to  fruit  in  the  mountain  region,  as 
noted  by  the  various  observers,  and  for  this  reason  the 
dates  and  periods  selected  will  be  taken  up  in  chrono¬ 
logical  order. 

The  greatest  damage  to  fruit  in  the  region  is  caused 
during  a  top  freeze,  and  particularly  is  this  true  when  a 
top  freeze  follows  a  period  of  a  week  or  more  during 
which  the  temperature  has  been  continuoulsy  above 
normal  and  the  fruit  buds  have  begun  to  swell  or  even 
open.  Well-marked  examples  of  this  condition  occurred 
March  28  and  29  in  the  spring  of  1913.  Immediately 
preceding  this  cold  spell  the  temperature  throughout  the 
mountain  region  was  considerably  above  the  normal, 
the  week  before  averaging  daily  an  excess  of  10°,  with 
maxima  ranging  from  65°  to  '75°  at  all  points  in  the 
region,  except  the  more  elevated  sections. 

This  warm  period  ended  on  March  27  and  was  followed 
by  a  marked  change  to  colder  with  norms  on  the  first 
of  the  two  dates  in  question  at  all  stations  except  Bryson, 
the  most  westerly  location,  and  general  inversions  on 
che  last  date.  With  the  exception  of  Transon,  Wilkes- 
boro,  Mount  Airy,  and  Tryon,  the  damage  done  by  the 
cold  high  winds  of  the  27tli-28th  and  by  the  freeze  of  the 
28th-29th  was  general,  and  the  buds  of  peaches,  pears, 
and  plums,  and  some  varieties  of  apples  were  so  damaged 
that  the  yield  as  a  whole  was  the  lowest  in  many  years. 
At  Blowing  Rock,  Highlands,  and  Transon  the  injury 
was  slight  as  compared  with  other  points,  and  it  is  prob¬ 
able  that  owing  to  the  high  elevation  of  the  orchards  at 
these  locations,  the  temperature  during  the  preceding 
warm  spell  did  not  reach  a  degree  sufficiently  high  to 
advance  the  fruit  buds  to  a  stage  where  they  wrere  suscep¬ 
tible  to  great  injury  by  the  following  cold.  However, 
at  these  high  altitudes  damage  is  very  likely  to  occur 
later  in  the  season,  when  the  fruit  is  farther  advanced 
and  when  orchards  at  lower  elevations  are  more  likely 
to  escape  injury.  In  fact,  as  late  as  May  11  and  12  in 
the  same  spring  killing  frosts  caused  great  damage  at 
Transon  and  Blowing  Rock.  In  the  Flat  Top  orchard 
in  the  latter  place  fruit  wras  killed  even  to  an  approximate 
height  of  60  feet  on  the  slopes,  and  at  station  No.  3 
during  this  two-day  period  in  May  the  temperature  fell 
to  23°  with  24  PIF°  on  the  11th,  and  to  29°  with  11  HF° 
on  the  12th. 

During  the  two-day  period  mentioned  above  the  num¬ 
ber  of  HF°  at  Mount  Airy,  Wilkesboro,  and  Tryon  was 
small  as  compared  with  those  at  other  stations,  although 
the  actual  temperatures  were  below  freezing.  On  the 
first  night  with  norm  conditions  the  number  of  HF°  was 
generally  greatest  at  the  summit  stations  and  least  at 
the  base,  while  on  the  second  night,  with  inversion 
conditions,  the  reverse  was  the  case.  This  relation  wnll 
be  found  to  exist  generally  during  all  cold  periods.  It 
will,  therefore,  be  seen  that,  broadly  speaking,  the  higher 


85 


THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 


levels  on  a  slope  experience  damage  from  top  freeze 
or  norm  conditions,  those  at  the  base  receive  injury 
from  frosts,  and  the  intermediate  positions  are  freer 
from  damage  by  either  freezes  or  frosts.  This  is  espe¬ 
cially  the  case  with  long  slopes. 

During  the  spring  of  1914  there  was  comparatively 
little  damage  to  fruit  in  any  section  of  the  mountain 
region,  and  the  condition  of  all  fruit  was  considerably 
above  the  average.  However,  at  Blowing  Rock  the 
apple  blooni  in  the  vicinity  of  No.  3  was  light  as  compared 
with  that  in  the  upper  portion  of  the  Flat  Top  orchard, 
and  it  is  thought  that  this  condition  was  a  result  of  the 
heavy  freeze  on  the  valley  floor  the  previous  year,  Mav 
11-12,  1913,  already  referred  to. 

With  the  exception  of  a  few  days  in  the  last  week  of 
March,  1914,  the  weather  was  abnormally  cold,  and  it  is 
very  likely  that  the  freedom  of  the  fruit  buds  from  injury 
was  then  due  to  the  fact  that  they  had  not  been  forced 
by  early  periods  of  growing  weather  such  as  occurred  in 
the  spring  of  1913.  The  only  period  during  the  spring 
of  1914  in  which  damage  could  have  occurred  was  that 
of  April  9-10,  in  which  the  estimated  peach  crop  at 
Blantyre  was  reduced  one-third.  In  this  period  norm 
conditions  were  general  on  the  first  day,  approaching 
inversions  at  most  stations  on  the  10th,  with  inversions 
generally  on  the  11th  at  all  stations. 

Combining  the  total  HF°  for  each  of  the  three  dates, 
the  largest  number  on  any  slope  generally  occurred  at 
the  higher  stations,  the  more  elevated  slopes  had  the 
greatest  number,  and  of  the  less  elevated  slopes,  Mount 
Airy,  Wilkesboro,  and  Tryon,  the  base  stations,  in  com¬ 
parison  with  the  respective  summits  had  the  greatest 
number  of  HF°.  This  is  mainly  because  the  slopes  at 
Mount  Airy  and  Wilkesboro  are  short  and  inversion 
conditions  predominate,  as  the  norm  frequency  depends 
almost  entirely  upon  tbe  length  of  slope  and  not  neces¬ 
sarily  upon  elevation  above  sea  level.  At  Tryon,  how¬ 
ever,  the  slope  is  considerably  longer  than  at  either 
Wilkesboro  or  Mount  Airy,  and  the  relatively  large 
number  of  HF°  at  the  base  station  during  this  period 
was  due  to  the  lack  of  a  breeze  down  the  valley  and  the 
prevailing  on-slope  winds  which  brought  quantities  of 
warm  air  to  the  stations  on  the  slope,  while  the  accumu¬ 
lation  of  cold  air  and  its  cooling  by  radiation  was  allowed 
to  continue  on  the  valley  floor  without  interruption,  thus 
ermitting  the  temperature  there  to  fall  several  degrees 
elow  freezing. 

During  this  April  period  in  1914  the  cold  stations  on 
the  slopes  at  Gorge  and  Hendersonville,  No.  2  in  each 
case,  had  the  greatest  number  of  HF°  on  their  respective 
slopes,  as  did  also  Mount  Airy  No.  3,  easterly  slope,  as 
compared  with  No.  2,  westerly  slope,  at  the  same  eleva¬ 
tion  above  the  base.  There  was  little  difference  between 
the  two  slopes  at  Asheville,  except  that  at  the  highest 
stations,  Nos.  3  and  3a,  where  the  number  of  HF°  at 
No.  3a  on  the  southerly  slope  was  30  less  than  at  the 
station  on  the  opposite  slope  at  the  same  elevation. 

In  the  autumn  of  1914  there  occurred  on  November 
20  and  22  a  notable  example  of  a  norm  followed  by  an 
inversion,  while  on  the  24th  and  25th  excellent  examples 
of  general  inversions  were  recorded,  with  the  temperatures 
at  most  of  the  higher  slope  and  summit  stations  consid¬ 
erably  higher  than  their  respective  base  Stations.  The 
minimum  temperatures  observed  on  November  20,  1914, 
were  the  lowest  noted  during  the  research  for  so  early  in 
the  season,  and  this  is  borne  out  by  the  large  number  of 
HF°  in  all  localities,  including  even  Tryon,  where  the 
lowest  minimum  was  11°  at  No.  4  with  a  total  number 
of  209  HF°.  When  severe  cold  during  norms  covers  the 


region,  the  degree  of  cold  depends  chiefly  upon  the  ele¬ 
vation  and  latitude. 

Under  date  of  November  22  there  was  a  general  de¬ 
crease  in  the  nuniber  of  HF°  with  increase  in  elevation — 
a  condition  typical  of  inversion  nights.  At  the  higher 
stations  on  several  of  the  slopes  the  temperature  did  not 
reach  the  freezing  point  at  all,  while  at  their  respective 
base  stations  the  minima  were  much  below  32°,  remain¬ 
ing  at  that  degree  for  several  hours.  At  Gorge,  Hender¬ 
sonville,  and  Blantyre,  for  instance,  the  contrast  between 
base  and  summit  stations  was  quite  pronounced,  the 
number  of  HF°  being,  respectively,  137  and  0,  174  and 
0,  and  202  and  1.  A  marked  effect  of  wind  direction  was 
noted  at  both  Bryson  and  Mount  Airy  in  that  the  HF° 
at  Nos.  2a  and  3,  respectively,  were  greater  than  at  the 
other  stations  of  the  same  elevation,  No.  2  in  each  case. 
There  is  ordinarily  little  difference  between  the  HF°  at 
Nos.  2  and  3  at  Mount  Airy,  respectively  on  westerly  and 
easterly  slopes,  and  the  southerly  slope  at  Bryson,  No.  2a, 
is  not  often  so  much  colder  than  No.  2  on  the  northerly 
slope  as  to  cause  a  difference  of  33  HF°,  as  recorded  on 
November  22.  In  fact,  at  Bryson  the  minimum  tem¬ 
perature  at  No.  2a  was  only  1°  lower  than  at  No.  2,  but 
the  temperature  at  the  former  station  reached  freezing 
an  hour  before  the  same  degree  was  recorded  at  No.  2, 
and,  under  the  influence  of  uninterrupted  cooling  by 
radiation,  fell  5°  lower,  reaching  27°  at  9  p.  m.  At  No.  2 
at  the  same  hour  the  temperature  rose  to  34°  under  the 
influence  of  light  northwest  winds,  bringing  warm  air  to 
the  slope,  while  No.  2a,  located  on  the  lee  side  of  the 
knob  with  reference  to  northwest  winds,  apparently  did 
not  receive  any  of  this  warm  air.  Toward  morning,  with 
diminishing  wind,  the  temperature  at  both  stations 
reached  their  respective  minima.  At  Mount  Airy  a  simi¬ 
lar  condition  prevailed  in  that  the  westerly  winds  pre¬ 
vented  the  temperature  from  remaining  at  a  low  point 
on  the  west  slope,  while  on  the  easterly  slope  loss  through 
radiation  continued  practically  all  night,  resulting  in 
low  minima. 

The  two  nights  of  November  24  and  25  were  typical  of 
general  inversions,  and  the  resulting  HF°  represent 
fairly  well  the  temperature  conditions  experienced  on  the 
various  slopes.  At  nearly  all  locations  the  greatest 
number  of  HF°  occurred  at  the  base  station,  decreasing 
rapidly  with  increase  in  elevation  up  the  slopes  to 
the  summit  stations,  where  practically  none  was 
recorded. 

The  spring  of  1915,  like  that  of  1914,  was  generally 
favorable  for  fruit  growing  in  the  mountain  region  as 
far  as  the  meteorological  conditions  were  concerned, 
although  some  damage  was  done  by  cold  winds  during 
March.  There  was  a  full  crop  of  peaches,  while  the 
yield  of  apples  was  very  light,  as  damage  from  blight 
occurred  in  most  sections,  except  at  Highlands,  where 
nearly  a  full  crop  was  reported.  At  Wilkesboro  also 
there  was  a  good  crop  of  both  peaches  and  apples. 

In  both  the  China  and  the  Flat  Top  orchards  at  Blowing 
Rock  the  apple  crop  was  a  complete  failure  in  1915, 
owing  to  an  unusually  heavy  hailstorm  on  April  23,  which 
knocked  off  the  buds  just  as  they  were  beginning  to  swell. 

During  the  period  from  October  9  to  12,  inclusive, 
1915,  there  occurred  an  example  of  an  early  cold  spell 
in  the  orchard  region,  with  norms  general  on  the  9th 
and  inversions  on  the  11th  and  12th,  part  of  the  stations 
reporting  the  former  and  part  the  latter  conditions  on  the 
10th.  Tryon  did  not  register  a  minimum  of  32°  during 
this  period,  except  at  the  top  station,  No.  4,  on  the  9th 
and  10th,  when  freezing  temperature  was  experienced 
on  each  night  for  one  hour. 


SUPPLEMENT  NO.  19. 


86 


The  spring  of  1916  was  quite  similar  to  that  of  1913, 
both  seasons  being  unfavorable  for  fruit  growing  in  the 
mountain  region.  There  were  several  periods  of  warm 
growing  weather  in  January  in  both  years,  followed  by 
much  colder  weather  in  February.  In  fact,  the  average 
temperature  for  January,  1913  and  1916,  exceeded  that 
for  the  respective  Februaries  by  6.2°  and  6.7°.  It  is 
this  very  condition — periods  of  growing  weather  in  the 
middle  of  winter,  forcing  the  fruit  buds  to  a  susceptible 
stage,  and  followed  later  in  the  season  or  in  early  spring 
by  cold  weather — which  kills  or  damages  the  buds  and 
seriously  affects  the  raising  of  fruit  at  the  higher  eleva¬ 
tions. 

As  stated  before,  January,  1916,  was  unusually  warm, 
the  average  daily  excess  in  temperature  above  the  normal, 
as  shown  by  the  records  at  the  Asheville  Weather  Bureau 
station  during  the  last  decade  being  17°,  with  maxima 
averaging  more  than  60°.  This  warmth  was  followed 
during  the  first  half  of  February  by  temperatures  slightly 
above  the  normal,  with  the  exception  of  a  few  days,  so 
that  at  the  beginning  of  the  second  decade  the  season  was 
several  weeks  early,  and  the  sudden  change  to  abnormal 


were  weak  in  character  and  limited  in  extent.  For  the 
period  as  a  whole  the  frost  intensity  was  therefore 
greatest  at  the  summit  stations,  except  at  points  having 
cold  base  stations,  such  as  Blantyxe  and  Bryson,  where 
the  frost  intensity  on  the  10th  was  much  greater  on  the 
valley  floor  than  it  was  at  the  summit  during  the  norm 
conditions. 

Reference  may  here  be  made  to  Figures  70,  71,  and  72, 
showing,  respectively,  the  average  number  of  HF°  at 
each  station  for  10  typical  inversions,  10  typical  norms, 
and  the  average  number  for  the  20  nights  of  both  condi¬ 
tions,  the  HFU  being  grouped  according  to  the  elevation 
of  the  various  stations  in  a  manner  similar  to  the  graphs 
discussed  under  “Inversions  and  norms  (figs.  47,  48,  and 
49.  As  the  relation  of  IiF°  to  average  minima  during 
these  conditions  is  generally  marked,  Tables  2  and  2a 
can  be  used  to  advantage  in  this  connection. 

There  is  great  variation  in  the  locations  on  the  various 
slopes  where  the  duration  of  the  minimum  temperature 
is  longest  or  shortest,  and  this  is  only  natural,  as  the 
duration  has  reference  to  the  actual  minima  observed 
at  the  individual  stations,  which,  of  course,  vary  con- 


cold  on  the  14th  practically  wiped  out  the  peach  crop 
throughout  the  region,  except  at  Tryon,  by  killing  the 
buds  which  had  been  brought  to  a  tender  condition. 
The  cold  continued  until  the  17th,  although  all  damage 
done  to  fruit  occurred  on  the  first  two  nights,  when 
norms  prevailed  generally.  By  the  16th  inversions 
appeared,  and  by  the  17th  only  the  colder  base  stations 
experienced  frost  intensity  of  any  importance. 

Another  cold  spell  occurred  in  1916  from  the  loth  to 
the  18th  of  March  and  caused  further  damage  to  the  peach 
crop  by  the  heavy  freeze  the  first  two  nights.  On  the 
18th  inversions  prevailed  on  all  slopes,  if  we  consider 
No.  la  at  Altapass  as  the  true  base  for  that  slope,  and  use 
for  it  the  HF°  value  at  Gorge  No.  1.  On  this  date  the 
HF°  at  No.  5  Altapass  and  Gorge  No.  1  were  50  and  60, 
respectively,  and  taking  the  whole  slope  at  Altapass 
from  No.  5  to  No.  la,  the  middle  of  the  thermal  belt 
is  seen  to  be  at  No.  2. 

In  the  spring  of  1916  still  another  period  of  cold 
weather  was  noted  in  April,  from  the  7th  to  the  10th, 
inclusive,  attended  by  strong  northwest  winds  and  con¬ 
siderable  snow  at  the  higher  elevations.  This  may  be 
considered  a  typical  norm  period  for  all  stations,  as  the 
inversions  which  occurred  on  the  10th,  the  last  day, 


siderably  on  any  slope.  For  instance,  the  minima 
might  be  24°  at  the  base,  28°  at  the  summit,  and  31° 
on  the  slope  midway  between,  and  the  length  of  time 
would  then  have  reference  to  these  particular  figures. 
While  it  might  be  expected  that  the  temperature  would 
remain  at  its  lowest  point  on  the  portion  of  the  slope, 
usually  marking  the  center  of  the  thermal  belt,  the  shortest 
time,  yet  when  it  is  considered  that  this  lowest  tempera¬ 
ture  is  31°  as  compared  with  24°  and  28°  at  the  base  and 
summit,  respectively,  it  is  not  strange  that  the  duration 
is  not  always  shorter  than  those  of  24°  and  28°.  Never¬ 
theless,  geographic  variation  in  the  HF°  values,  repre¬ 
senting  both  the  duration  and  the  degree  of  frost,  conform 
rather  closely  to  the  variation  in  minimum  temperature. 

Under  inversion  conditions  (fig.  70)  the  largest  number 
of  HF°  for  the  entire  region  is  shown  to  be  173  at  station 
No.  3  in  the  small  frost  pocket  in  the  Waldheim  orchard 
at  Highlands,  where  the  lowest  absolute  minimum  and 
the  lowest  average  minimum  were  registered,  and  the 
smallest  number  was  4  at  station  No.  2  on  the  slope  at 
Tryon,  also  the  point  of  highest  minimum,  both  absolute 
and  average.  Highlands  is  in  the  group  of  the  highest 
altitude  and  Tryon  in  the  group  of  lowest  altitude  above 
sea  level.  In  every  case  by  far  the  largest  number  of 


87 


THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 


HF°  is  found  to  be  at  the  base  station,  provided  such 
station  was  located  on  a  valley  floor.  The  figures  for 
Altapass  are  consistent,  as  its  station  No.  1  is  just  as  much 
a  slope  station  as  Nos.  2,  3,  and  4,  and  the  increasing 
number  of  HF°  at  the  higher  levels  of  the  slope  is  of 
course  due  to  the  great  surface  area  in  the  vicinity  of 
the  summit. 

Under  norm  conditions  (fig.  71),  the  stations  of  highest 
altitude  have  the  greatest  number  of  IIF°;  or  at  least 
this  holds  true  for  each  group,  but  for  the  groups  as  a 
whole  there  is  some  variation.  For  instance,  station 
No.  4,  at  Cane  River,  has  the  largest  number  of  HF°,  2G2, 
with  smaller  amounts  at  the  summit  stations  of  greater 
altitude,  as  Ellijay,  Blowing  Rock,  and  Highlands. 
The  smallest  number  of  HF°  for  all  the  stations,  as 
shown  by  Figure  71,  is  39  at  the  base  station  at  Tryon,  the 
station  of  lowest  altitude  above  sea  level.  In  the  indi¬ 
vidual  groups  there  is  in  most  places  a  steady  increase  in 
HF°  from  the  base  to  the  summit  during  norms,  and 
Ellijay  is  the  only  place  where  the  base  station  has  a 
larger  number  of  HF°  than  the  station  immediately 
above  on  the  slope. 


long  ones  as  well.  It  has  already  been  explained  how 
the  height  of  the  center  of  the  thermal  belt  varies  on 
different  slopes  and  on  different  nights  of  inversion, 
depending  upon  topography  and  various  metorological 
factors. 

The  verdant  zone  may  be  designated  as  the  portion  of 
a  slope  in  the  spring  and  fall  where  the  foliage  remains 
fresh  and  green,  having  been  untouched  by  frost  ox- 
freezing  temperature,  while  the  foliage  on  other  portions 
of  the  slope  lower  down  and  sometimes  higher  up  has 
suffered  damage.  A  verdant  zone  has  been  considered 
by  many  writers  as  a  belt  400  or  500  feet  in  width  a 
variable  distance  above  the  valley  floor;  but  such  a  zone, 
while  having  a  lower  limit  on  a  slope,  may  actually 
extend  to  the  summit,  the  latter  being  its  upper  limit. 

A  vei’dant  zone  may  develop  on  a  long  slope  on  a  single 
night  of  inversion  when  the  temperature  falls  to  freezing 
or  below  in  the  upper  as  well  as  the  lower  levels,  leaving 
a  neutral  zone  untouched,  and  tiffs  is  characteristic  of  a 
slope  having  great  area  at  the  summit,  such  as  Tryon 
and  Altapass.  It  may  form  in  the  upper  levels  on  a  night 
of  invei'sion  when  frost  occurs  in  the  lower  levels  with 


In  Figure  72,  portraying  the  total  number  of  HF° 
during  selected  noi’m  and  inversion  periods  combined, 
generally  speaking,  the  groups  having  the  lowest  altitude 
above  sea  level  have  the  smallest  number  and  those  having 
the  highest  altitude  the  largest  number.  There  is 
considerable  variation  in  each  group,  sometimes  the 
greatest  number  being  at  the  base  and  sometimes  at 
the  summit,  but  the  smallest  number  is  never  on  the 
vallev  floor,  but  either  on  the  slope  or  at  the  summit. 
For  the  entire  region  the  smallest  number  is  50  at  station 
No.  2  on  the  Tryon  slope  and  the  greatest  number,  377, 
at  the  base  station  No.  3  at  Highlands. 

VERDANT  ZONES. 

Some  reference  has  been  made  to  the  subject  of  vei’dant 
zones  in  the  Introduction.  Ordinarily,  the  terms 
“thermal  belt”  and  “verdant  zone”  would  be  considered 
synonymous;  but  the  latter  is  the  result  of  special 
thermal  conditions,  rather  than  the  thermal  conditions 
themselves. 

A  thermal  belt  is  the  portion  of  a  slope  above  the  valle} 
floor  that  has  relatively  high  night  temperatures,  usually 
reaching  the  summits  of  short  slopes  and  often  those  of 


the  thermal  belt  above  reaching  to  the  summit,  or  it 
may  form  in  the  lower  levels  during  a  top-freeze  condition, 
or  it  may  be  the  result  of  a  combination  of  inversion  and 
top-freeze  conditions  over  a  period  of  two  or  more  nights. 
It  can  be  readily  understood  that  on  short  slopes  norms 
can  not  be  considered  a  factor,  as  the  temperature  varies 
very  little  there  from  the  summit  downward,  usually 
no  more  than  a  degree  or  two,  and  if  freezing  occurs  at 
the  summit  it  is  quite  likely  to  prevail  over  the  entire 
slope  down  to  the  valley  floor. 

The  Tryon  slope  seems  to  be  more  favorable  than  any 
other  for  the  formation  of  a  verdant  zone,  because  the 
slope  is  fairly  long,  it  has  no  opposing  slope  and  therefore 
the  belt  of  highest  temperature  is  low,  and  the  area  at 
the  summit  is  great,  resulting  in  relatively  low  tempera¬ 
ture  in  the  higher  levels.  . 

The  best  example  of  verdant  zone  conditions  on  a 
sino-le  night  at  Tryon  duting  the  four  years’  record  was 
observed  April  9-10,  1915,  when  the  temperature  at 
No.  2  was  from  1°  to  3°  above  freezing  and  the  tem¬ 
perature  at  both  Nos.  1  and  4  ranged  between  20  and 
28°  as  shown  in  Figure  73,  the  black  portions  in  the 
upper  part  of  the  graph  illustrating  the  length  of  time 


88 


SUPPLEMENT  NO.  19. 


freezing  temperature  prevailed  on  the  slope  above  and 
below  the  verdant  zone.  Figure  73  (lower  part  of  graph) 
also  shows  the  vertical  temperature  gradient  at  4  a.  m. 
on  the  9th,  as  well  as  at  midnight  of  the  9th-10th,  the 
portion  of  the  curve  on  each  night  to  the  right  of  32° 
fine  representing  the  verdant  zone  and  that  portion  of 
the  slope  where  the  minimum  during  these  nights  did 
not  fall  below  32°.  At  midnight  on  the  night  of  the 
8th-9th,  the  verdant  zone  was  unusually  wide,  the 
lower  limit  reaching  almost  down  to  No.  1  and  the  upper 
limit  a  little  over  halfway  between  Nos.  3  and  4 — 
probably  a  distance  of  750  feet.  At  2  a.  m.  the  zone 
was  reduced  to  its  normal  width  by  the  lowering  of  the 
temperature  at  all  stations  except  No.  1,  the  reading  at 
No.  2,  however,  still  remaining  above  freezing. 

Figure  73  illustrates  the  temperature  distribution  on 
the  slope  at  Tryon  during  the  formation  of  a  verdant 
zone.  The  portions  of  the  thermograph  traces  falling 
below  the  freezing  point  have  been  shaded.  The  lower 
portion  of  the  graph  shows  the  vertical  temperature 
gradients  during  the  critical  hours  on  each  night,  also 
the  approximate  width  of  the  resulting  verdant  zones. 

There  were  several  other  instances  at  Tryon  in  the 
spring  and  fall  during  the  four-year  period  of  the  research 


Fig.  74. — Possible  variation  in  limits  of  verdant  zone  on  mountain  slopes. 

when  the  conditions  were  favorable  for  the  formation 
of  a  verdant  zone. 

On  the  night  of  October  21,  1913,  during  an  inversion 
the  temperature  was  freezing  or  below  at  all  stations  on 
the  slope  down  to  No.  2,  and  practically  the  same  con¬ 
dition  occurred  on  October  31  and  November  1  following, 
and  it  was  not  until  20  days  thereafter  that  there  was  a 
general  freeze. 

In  the  spring  of  1914,  on  April  10,  a  freeze  occurred  at 
station  No.  4  and  frost  at  No.  1,  with  relatively  high 
temperature  on  the  slope  at  stations  Nos.  2  and  3,  thus 
favoring  the  formation  of  a  wider  verdant  zone  than  in 
the  preceding  autumn. 

In  the  autumn  of  1914  conditions  were  favorable  for 
the  formation  of  a  verdant  zone  on  the  night  of  October 
28,  much  the  same  as  in  the  autumn  of  1913. 

In  the  autumn  of  1915  a  top  freeze  occurred  at  Tryon 
on  October  9  and  10,  at  No.  4,  but  it  was  not  until 
November  4  that  the  temperature  fell  to  the  frost  point 
on  the  valley  floor  at  No.  1.  Later,  on  November  16, 
the  temperature  fell  to  freezing  on  the  slope  from  summit 
down  to  No.  3,  and  a  general  freeze  did  not  occur  until 
November  30.  As  a  consequence  a  wide  verdant  zone 
apparently  formed  in  the  early  portion  of  the  autumn 
period,  but  it  was  considerably  narrowed  later. 


In  the  spring  of  1916,  after  a  month  of  growing 
weather,  freezing  temperature  occurred  on  April  9  and 
10  from  summit  down  to  No.  3,  and  frost  simultaneously 
at  No.  1  in  the  valley  floor,  thus  favoring  the  formation 
of  a  verdant  zone  around  station  No.  2. 

Generally  speaking,  there  is  a  tendency  toward  the 
formation  of  a  verdant  zone  on  the  Tryon  slope  in  the 
spring  and  autumn,  300  or  400  feet  in  width,  with  the 
lower  limit  about  300  feet  above  the  valley  floor.  How¬ 
ever,  the  limits  of  this  zone  are  seldom  clearly  defined,  as 
they  vary  irregularly  on  the  slope,  just  as  the  temperature 
varies. 

The  line  of  demarcation  on  any  slope  between  verdant 
and  frosted  foliage  is  not  clearly  cut,  although  such 
claims  have  often  been  made.  It  has  been  stated  even 
that  photographs  of  certain  slopes  would  show  this 
phenomenon  distinctly,  but  it  must  be  conceded  that 
during  the  period  of  the  research  it  was  not  possible  to 
find  any  slope  so  well  marked,  there  usually  being  a 
gradual  merging  of  the  green  and  frosted  foliage. 

It  has  been  pointed  out  previously,  especially  under 
the  discussion  of  “  Average  minimum  temperature  and 
inversion”  that  the  minima  on  any  slope  vary  decidedly 
with  topography  and  surrounding  vegetation,  depending 
on  the  relative  steepness  of  the  slope,  proximity  to 
neighboring  slopes  and  timber,  the  relative  area  at  the 
summit,  the  character  of  the  valley  floor,  and  the  extent 
and  density  of  the  soil  cover,  so  that  at  different  points 
of  the  same  elevation  on  any  slope  there  is  often  great 
differences  in  minimum  temperature,  and  consequently 
the  line  between  safety  and  injury  is  sure  to  be  more  or 
less  ragged. 

Figure  74  may  represent  the  limits  of  a  verdant  zone 
possible  on  mountain  slopes  having  great  variation  in 
topography  and  vegetation.  Here  the  term  “verdant 
zone”  is  used  in  the  larger  sense  and  includes  all  cases 
where  a  portion  of  the  slope,  whether  large  or  small,  high 
or  low,  is  untouched  by  frost  or  freezing  temperature. 
The  relative  length  and  position  of  the  white  columns 
indicate  roughly  the  position  and  width  of  verdant  zones 
under  varying  conditions  of  topography  and  weather. 

x  represents  a  zone  on  any  long  slope  forming  after  a 
top  freeze  when  a  temperature  of  32°  was  not  felt  below 
the  height  of  700  feet.  The  other  lettered  divisions  in¬ 
dicate  conditions  resulting  from  inversions,  or  inversions 
and  norms  combined :  a,  an  average  condition  with  mod¬ 
erate  slope  and  moderate  vegetation;  b,  a  steep  slope  at 
“c,”  widening  still  further  because  of  increasing  grade 
and  bare  vegetation;  at  d,  because  of  change  to  gentle 
slope  with  dense  vegetation,  the  lower  limit  of  the  belt 
rises  and  it  falls  again  at  e  with  decreasing  vegetation; 
f,  in  a  cove  with  moderate  vegetation  and  less  opportunity 
for  interchange  with  the  warm  free  air,  the  lower  limit 
again  rises  and  the  zone  narrows  still  further  at  g,  which 
marks  the  location  of  a  sink  or  frost  pocket,  with  dense 
vegetation.  It  then  falls  to  the  limits  marked  by  a, 
a  moderate  slope  with  moderate  vegetation  and  at  h  is 
apparent  the  effect  of  opposing  slopes  in  close  proximity 
in  the  narrowing  of  the  belt,  while  at  the  point  i,  where 
there  is  no  opposing  slope  and  small  area  at  the  summit, 
there  is  a  widening  of  the  belt;  and,  finally,  at  k ,  with  no 
opposing  slope  but  great  area  near  the  summit,  the  belt 
narrows  again,  the  latter  conforming  to  the  conditions 
found  at  Tryon. 

It  may  be  said  that  the  conditions  portrayed  are  purely 
ideal  and  could  not  actually  be  found  on  any  single  slope, 
and  this  is  true.  But  the  variation  is  not  beyond  the 
realm  of  possibility  in  a  series  of  slopes,  and  there  might 
even  be  additional  variations. 


THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 


Rise  in  temperature  at  summit  stations  earlier  than  on  the 
valley  floor— The  statement  is  sometimes  made  by  mete¬ 
orologists,  in  their  studies  of  mountain  and  valley  condi¬ 
tions,  that  the  temperature  at  the  summit  usually  rises 
before  that  at  the  base.  Perhaps  the  observations  7  of 
Prof.  McLeod,  of  McGill  University,  were  the  first  made 
in  America  along  this  line,  embracing  a  study  of  the  rises 
in  temperature  at  the  base  and  summit  of  Mount  Royal, 
Montreal.  Of  course  the  diurnal  rise  naturally  occurs 
earlier  in  the  morning  at  the  summit  than  at  the  base, 
as  the  sun  strikes  the  higher  points  first,  but  it  is  not  with 
this  diurnal  change  that  we  have  to  do  in  this  discussion. 
McLeod  concluded  that  it  was  possible  to  make  tempera¬ 
ture  forecasts  24  hours  in  advance  at  Montreal  by  noting 
the  changes  at  the  summit  of  Mount  Royal,  and  he 
claimed  a  verification  of  78  per  cent  by  tins  means. 
The  summit  of  Mount  Royal  is  620  feet  above  its  base 
and  800  feet  above  sea  level. 

Clayton  8  made  some  studies  along  the  same  line  at 
Blue  Hill  observatory  in  Massachusetts  several  years  ago 
and  found  variations  much  the  same  as  those  observed 
by  McLeod.  Blue  Hill  has  an  altitude  of  640  feet  above 
sea  level,  the  summit  being  590  feet  above  the  valley 
floor. 

Church  and  Fergusson  in  their  recent  studies  9  of  tem¬ 
perature  conditions  on  Mount  Rose,  Nevada,  at  a  much 
greater  elevation,  did  not  find  such  a  variation,  and  they 
concluded  that  Mount  Rose  was  not  favorably  situated 
for  the  occurrence  of  this  phenomenon. 

The  studies  in  this  research  in  the  North  Carolina  moun¬ 
tain  region,  moreover,  did  not  show  results  similar  to 
those  obtained  by  McLeod  and  Clayton.  In  fact,  the 
observations  provided  no  data  upon  which  such  tempera¬ 
ture  forecasts  24  hours  in  advance  could  be  based.  As  a 
rule,  the  temperature  rose  one  or  two  or  three  hours  ear¬ 
lier  at  the  summit  than  at  the  base,  sometimes  even  rising 
at  the  higher  levels  when  it  was  falling  on  the  valley  floor; 
but  rarely  was  the  rise  at  the  summit  levels  24  hours  in 
advance  of  the  rise  at  the  base. 

In  the  study  of  the  North  Carolina  data  it  is  found 
that  the  temperature  rarely  rises  at  the  summit,  even 
where  the  peaks  are  isolated,  more  than  10  hours  earlier 
than  on  the  valley  floors,  and  the  average  does  not 
exceed  four  hours.  Of  course,  Mount  Royal  and  Blue 
Hill  are  more  isolated  than  the  mountain  peaks  of 
North  Carolina,  and  this  might  be  considered  an  addi¬ 
tional  reason  for  the  early  rises,  although  the  elevation 
of  these  northern  peaks  is  relatively  slight.  Possibly  the 
more  active  wind  movement  generally  in  the  northern 
sections  is  also  a  factor. 

The  temperature  changes  in  the  higher  levels  of  the 
Carolina  mountain  region  certainly  furnish  no  basis  for 
the  making  of  temperature  forecasts,  as  found  by 
McLeod  and  Clayton,  and  the  results  are  in  agreement 
with  those  obtained  by  Church  and  Fergusson  for 
Mount  Rose.  Apparently  the  conclusions  of  McLeod  and 
Clayton  have  been  accepted  by  meteorologists,  but  it  is 
thought  that  their  data  should  now  be  more  completely 
examined  and  verified  in  view  of  the  more  recent  studies 
on  the  subject. 

Many  instances  have  been  noted  in  this  research  of 
rises  in  temperature  several  hours  earlier  at  the  summit 
than  on  the  valley  floor  and  some  instances  even  when 
the  temperature  was  still  falling  on  the  floor.  While 
such  rises,  although  sometimes  slight,  have  been  noted 
on  all  slopes,  those  of  large  range  are  only  observed  on 


i  Transactions  of  the  Royal  Society  of  Canada,  series  1904-1909. 

»  Clayton,  H.  if.,  Blue  Kill  Observatory  Bulletins,  No.  1,  1899,  No.  Ijl900. 

9  Bui.  S3,  Technical  University  of  Nevada  Agricultural  Experiment  Station,  1915. 


isolated  knobs  so  located  as  to  be  free  from  obstructions 
in  the  shape  of  high  elevations  to  the  south  and  east. 
Thus  Cane  River  stands  out  as  the  most  prominent  of 
the  points  in  this  research  showing  the  early  rises  at  its 
summit.  Slopes  like  Altapass  and  Tryon,  which  have 
great  area  near  their  summits,  and  Ellijay,  to  the  south¬ 
east  of  which  lies  the  Highlands  Plateau,  show  these 
rises  in  a  less  degree. 

Such  rises  in  temperature  result  in  unusual  inversions 
and  these  occur  in  connection  with  the  Intermediate  and 
the  Cyclonic  Types  of  inversion.  In  the  Cyclonic  Type 
the  early  temperature  rise  at  the  summit  is  primarily 
due  to  rather  fresh  southerly  or  southeasterly  winds, 
which  have  developed  in  the  advance  of  the  approaching 
low  before  this  air  movement  has  started  at  the  base, 
surface  friction  retarding  the  free  movement  of  the  air 
at  the  lower  levels.  In  the  Intermediate  or  Recovery 
Type,  as  the  high  pressure  begins  to  pass  to  the  eastward 
from  the  region  the  stations  at  the  higher  levels  feel  the 
rise  in  temperature  first  under  the  influence  of  light 
south  to  east  winds,  the  hills  preventing  the  cold  air  in 
the  lower  levels  from  draining  away. 


Fig.  75. — Thermograph  traces,  November  12-13, 1913,  stations  Nos.  1  and  5,  Gorge. 

Examples  of  both  types  are  numerous,  but  limited 
space  permits  but  three  illustrations,  those  of  Cane 
River,  January  27-28,  1914  (fig.  58),  and  December 
19-23,  1916  (fig.  59),  both  of  which  have  already  been 
referred  to,  and  Gorge,  November  11-13,  1913  (fig.  75) 

Figure  59  includes  the  state  of  weather  and  the  direc¬ 
tion  and  velocity  of  the  wind  as  shown  by  the  records  at 
the  regular  Weather  Bureau  station  at  Asheville,  which 
is  located  only  about  25  miles  distant  from  Cane  River. 
It  illustrates  two  sets  of  conditions  attending  the  early 
warming  up  of  the  summit  station;  the  Cyclonic  Type  on 
the  19th-20th,  when  warm  southeast  winds  were  brought 
to  the  summit  by  the  development  of  a  low  to  the 
southwest;  and  the  Intermediate  Type,  on  the  22d- 
23d,  when  the  rise  in  temperature  following  a  cold  wave 
began  at  the  summit  first  without  the  immediate  in¬ 
fluence  of  an  approaching  low.  The  effect  of  wind 
direction  and  velocity,  as  well  as  that  of  state  of  weather, 
is  apparent  in  the  comparison  of  the  Asheville  wind  record 
with  these  temperature  traces.  On  the  morning  of  the 
18th,  a  low  moved  rapidly  over  the  region  toward  the 
northeast,  this  condition  causing  rapid  rises  in  tempera¬ 
ture  during  the  afternoon  and  night.  On  the  19th  the 
influence  of  a  low  approaching  from  the  northwest  began 
to  be  felt  at  the  summit  station,  while  on  the  20th  the 
temperature  rose  generally,  the  low  remaining  over  the 
region  and  the  temperature  being  high  throughout  the 


90 


SUPPLEMENT  NO.  19. 


21st;  but  on  the  morning  of  the  22d  the  low  moved 
away  closely  followed  by  a  high  which  had  already 
caused  24-hour  temperature  falls  of  20°  to  30°  in  the 
adjoining  States  to  tne  west.  The  approach  of  this  cold 
wave  gave  rapid  temperature  falls  at  Cane  River, 
especially  at  the  lower  stations,  but  by  the  late  afternoon 
the  recovery  had  begun  at  the  top  station,  about  14  hours 
ahead  of  the  rise  at  the  base  station.  One  of  the  out¬ 
standing  features  shown  in  Figure  59  is  the  almost  steady 
rise  in  temperature  at  the  summit  station  from  about 
10  p.  m.,  December  19,  to  noon,  December  21,  from  a 
minimum  of  18°  to  a  maximum  of  51°,  while  during  that 
period  there  were  two  distinct  and  separate  falls  at  the 
base  station  to  2°  at  5  a.  m.,  December  20,  and  to  31°  at 
7  a.  m.,  December  21,  with  an  intervening  rise  to  a  maxi¬ 
mum  of  44°.  It  seems  remarkable  that  such  a  pro¬ 
nounced  variation  in  temperature  could  persist  for  so 
long  a  period  of  time  within  such  a  small  radius,  the 
vertical  height  of  this  slope  being  only  1,100  feet.  The 
wind  direction  during  practically  the  entire  period  was 
from  the  south  and  southeast,  with  varying  force,  light 
and  gentle  during  some  hours  and  moderate  to  fresh  in 
others,  indicative  of  unstable  conditions. 

The  large  inversion  of  31°  at  the  summit  of  the  Gorge 
slope,  1,000  feet  above  the  base  station,  November  12-13, 
1913  (fig.  75),  is  the  greatest  of  all  observed  in  the  entire 
research,  but  an  inversion  almost  as  great,  30°,  occurred 
at  Cane  River  January  28,  1914  (fig.  58).  In  the  latter 
instance  the  temperature  did  not  begin  to  rise  at  the 
base  station  until  13  hours  after  it  had  begun  to  rise  at 
the  summit.  Both  are  examples  of  the  intermediate  type 
of  inversion. 

These  graphs,  illustrating  the  early  rise  in  temperature 
at  the  summit  as  compared  with  the  base,  are  supple¬ 
mented  by  Table  23,  giving  for  Cane  River,  Gorge, 
Globe,  and  Ellijay,  with  their  summits  ranging  from 
1,000  to  1,760  feet  above  the  floors,  data  in  tabular  form 
which  may  be  considered  as  representative  of  extreme 
instances  of  the  phenomenon  where  the  temperature 
was  rising  at  the  summit  at  the  time  it  was  falling  at  the 
base.  Examples  could  also  be  included  where  the  tem¬ 
perature  was  not  falling  at  the  base  were  space  available 
for  the  purpose. 

According  to  Table  23,  these  rises  are  much  more  fre¬ 
quent  at  Cane  River  summit  than  on  any  of  the  others, 
and  the  rise  there  begins  relatively  much  earlier,  doubt¬ 
less  because  of  the  comparatively  isolated  position  of  its 
summit.  Once  the  rise  at  Cane  River  summit  began  14 
hours  in  advance  of  that  at  the  base,  and  at  another  time 
13  hours  in  advance;  but  these  are  the  greatest  observed. 
Ellijay,  the  most  elevated  and  showing  one  rise  12  hours 
in  advance,  comes  next  in  order.  The  latter  point  does 
not  have  the  same  frequency  or  range  as  Cane  River, 
probably  because  of  its  location  in  the  midst  of  mountains 
of  equal  or  greater  height  and  because  the  Highlands 
plateau  of  equal  elevation,  with  Mount  Satulah  and 
Whiteside  Mountain  towering  above,  lies  to  the  south 
and  southeast  directly  in  the  path  of  these  warm  winds. 
Gorge,  next  in  order,  has  its  summit  station  on  an  isolated 
peak,  but  other  mountains  in  all  directions,  even  higher, 
are  not  far  distant.  The  table  includes  in  its  list  in¬ 
stances  of  the  largest  inversions  noted  during  the  re¬ 
search,  and  it  may  be  seen,  by  comparing  columns  a  and 
b  that  the  temperature  in  every  case  was  falling  decid¬ 
edly  on  the  floor  while  rising  at  the  summit,  and  the  table 
further  shows  (column  c)  that  even  in  these  extreme  in¬ 
stances  the  rise  at  the  summit,  on  the  average,  began  less 
than  nine  hours  earlier  than  on  the  floor. 


Table  23.— Most  pronounced  rises  in  temperature  at  selected  summit 
stations  at  the  time  falling  at  the  base. 


Station. 

Date. 

a 

b 

C 

Cane  River,  No.  4 . 

Nov  6-7,  1913 

19 

5 

6 

Ellijay,  No!  4  1 . 

Nov.  11-12,  1913. 

21 

12 

12 

Gorge,  No.  5 . 

Nov  12  13'  1Q13 

31 

14 

9 

Globe,  No.  3 . 

..  ..do 

25 

9 

8 

Cane  River,  No.  4 . 

.Ian.  27-28,  1914.. 

30 

14 

13 

Do . 

Feb.  2-3,  1914  . 

17 

8 

8 

Globe,  No.  3 . . 

Feb.  3-4 1  1914. 

13 

5 

4 

Gorge  No.  5 . 

17 

3 

Ellijay,  No.  5 . 

Feb.  16-17,  1914 

12 

10 

8 

Do . 

Mar.  2-3,  1914... 

10 

7 

9 

Cane  River,  No.  4 . 

Dec.  6-7,'  1915. 

19 

14 

10 

Do . 

Jan.  3-4,  1916... 

21 

7 

8 

Do . 

Dec.  6-7,  1916... 

22 

7 

8 

Do . 

Jan.  9-10,  1916.  . 

20 

8 

8 

Do . 

Dec.  19-20,  1916 

24 

4 

7 

Do . 

Dpp.  22-23.  1916 

22 

12 

14 

1 

1  No.  5  at  Ellijay  not  in  operation;  No.  4  located  1,240  feet  above  base  station. 

(a)  Greatest  difference  at  any  hour  (degrees)  between  base  and  summit  stations. 

(b)  Amount  of  rise  (degrees)  at  summit  station  from  sunset  to  sunrise. 

(c)  Number  of  hours  temperature  rose  at  summit  station  before  rise  began  at  base 
station. 

Elevations  of  summit  stations  above  respective  base  stations:  Cane  River  No.  4,  1,100 
feet;  Ellijay  No.  5,  1,760  feet;  Gorge  No.  5,  1,040  feet;  Globe  No.  3,  1,000  feet. 


DEW  POINT  AND  ENSUING  MINIMUM  TEMPERATURE. 

No  study  of  minimum  temperatures  in  a  field  research 
seems  to  be  complete  without  a  comparison  of  the  even¬ 
ing  dew  point  and  the  ensuing  minimum.  It  has  long 
been  supposed  that  a  relation  exists  between  the  dew 
point  and.  the  minimum  and  that  the  temperature  would 
not  fall  any  night  lower  than  the  dew  point,  so  that,  if 
the  point  of  condensation  were  higher  than  32°,  frost 
should  not  be  expected,  because  the  dew  point  having 
been  reached,  latent  heat  would  be  given  off  in  the  process 
of  condensation  and  a  further  fall  in  temperature  pre¬ 
vented.  Moreover,  the  loss  of  heat  by  radiation  from  the 
ground  is  more  rapid  through  dry  air  than  through  moist 
air,  and  as  a  consequence  when  the  humidity  is  high  in 
the  evening  the  temperature  the  following  night  is  not 
likely  to  fall  to  a  low  point  before  morning,  while  if  the 
humidity  is  low  the  temperature  will  fall  considerably. 
This  much  we  know,  of  course,  and  due  allowance  must 
be  made  for  the  vapor  pressure  in  estimating  the  ensuing 
minimum  temperature.  Attempts  have  been  made  to 
determine  with  some  exactness,  through  the  use  of 
formulas,  the  point  which  the  minimum  will  reach. 
Those  prepared  by  Prof.  J.  Warren  Smith  and  Charles  A. 
Donnel,  of  the  U.  S.  Weather  Bureau,  applicable  to  a  flat 
or  rolling  country  without  great  differences  in  elevation, 
have  received  considerable  attention.10 

However,  formulas  have  not  proved  of  any  material 
assistance  in  determining  the  ensuing  minima  to  the 
leader  of  this  project  in  the  special  regions  in  which  he 
has  conducted  field  work.  In  the  research  in  the  Wis¬ 
consin  cranberry  marshes  11  he  found  that  the  reading  of 
the  dew  point  in  itself  did  not  indicate  even  approxi¬ 
mately  the  point  to  which  the  minimum  would  fall. 
The  minimum  temperature  for  the  seasons  of  1906  and 
1907  in  one  section  of  a  bog  at  Mather,  Wis.,  averaged, 
respectively,  8.2°  and  7.6°  lower  than  the  dew  point 
readings  of  the  previous  evening  at  6  o’clock.  On  several 
nights  the  temperature  fell  20°  below  the  dew-point, 
and  on  one  night  it  was  even  28°  lower  in  spite  of  the  fact 
that  the  relative  humidity  on  the  bog  early  the  previous 
evening  was  as  high  as  94  per  cent.  The  humidity  in  a 
cranberry  bog  region  is  naturally  high,  but  it  is  probable 
that  a  short  distance  above  it  is  much  lower.  Often  the 


10  Smith  J.  Warren,  in  Predicting  Minimum  Temperatures,  Monthly  Weather 
Review,  Supplement  16. 

11  Bulletin  T,  Weather  Bureau,  1910,  by  Henry  J.  Cox. 


91 


THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 


blanket  of  fog  overlying  a  bog  docs  not  reach  higher  than 
30  or  40  feet,  the  humidity  above  it,  doubtless,  being 
comparatively  low,  and  thus  rapid  loss  of  heat  is  possible 
by  radiation  through  the  air,  and  the  temperature  in  the 
levels  below  is  reduced  to  a  critical  point. 

As  explained  in  previous  pages  in  the  description  of 
stations  employed  in  the  North  Carolina  research,  the 
home  station  in  each  group  was  supplied  with  a  sling 
psychrometer  in  addition  to  the  regular  equipment,  and 
for  purposes  of  convenience  this  station  was  nearest  to 
the  residence  of  the  observer,  regardless  of  whether  its 
shelter  was  on  the  valley  floor,  the  slope,  or  the  summit. 
The  home  stations  are  slope  stations  at  Altapass,  Ellijay, 
Highlands,  and  Tryon;  valley-floor  stations  at  Ashe¬ 
ville,  Blantyre,  Bryson,  Cane  River,  Globe,  Gorge,  Mount 
Airy,  and  Transon;  and  summit  stations  at  Blowing 
Rock,  Hendersonville,  and  Wilkesboro.  There  is  con¬ 
siderable  similarity  in  the  exposure  of  the  slope  stations, 
but  there  is  a  wide  variation  in  the  character  of  the  con¬ 
ditions  at  the  valley-floor  stations,  and  those  can  hardly 
be  considered  comparable  one  with  another.  For  in¬ 
stance,  Asheville,  which  is  located  in  a  cut  between  two 
slopes,  is  itself  on  an  incline  along  Bull  Creek,  while  the 
base  stations  at  Gorge  and  Bryson,  although  on  true 
valley  floors,  have  environment  much  different. 

Wet-bulb  readings  were  made  regularly  at  sunset, 
but  there  was  naturally  great  variation  in  the  results 
because  of  the  different  positions  of  the  home  stations 
at  each  place.  There  were  individual  instances  where 
the  minimum  temperatures  on  the  slope  were  20°  to 
30°  higher  than  the  previous  evening  dew  point,  while 
on  the  valley  floors  the  minima  were  correspondingly 
low.  For  instance,  at  Tryon  at  No.  2,  the  home  station 
on  the  slope,  the  dew  point  at  sunset  May  3,  1913,  was 
33°,  and  the  minimum  at  the  same  station  during  the 
night  was  67°;  again,  on  the  evening  of  April  4,  the  dew 
point  at  Bryson  No.  1,  the  home  station  on  the  valley 
floor,  was  67°,  the  minimum  during  the  night  reaching 
the  low  point  of  35°.  In  one  case  the  minimum  exceeds 
the  previous  evening  dew  point  by  34°,  and  in  the  other 
case  the  dew  point  exceeds  the  minimum  by  32°. 

Dew-point  values  have  been  computed  from  the 
wet-bulb  readings  made  at  sunset  for  the  year  1914, 
and  the  average  depression  of  the  minimum  temperature 
below  the  previous  evening  dew  point  at  each  place  is 
shown  by  months  in  figure  76, illustrating  (a)  the  average 
monthly  variation  for  all  15  home  stations  combined; 
(b)  for  the  home  stations  on  slopes,  and  (c)  for  the  home 
stations  on  valley  floors.  The  home  stations  at  Blowing 
Rock,  Hendersonville,  Highlands,  and  Wilkesboro,  with 
environments  so  different  from  the  other  stations  on 
slopes  and  valley  floors,  have  not  been  included  in  the 
comparison  shown  in  this  figure  by  the  curves  ( b )  and  ( c ). 

The  minimum  temperature  for  all  the  home  stations 
regardless  of  location  averages  below  the  previous  even¬ 
ing  dew  point  in  all  months  except  May,  curve  (a), 
this  being  the  month  when  inversions  are  found  with 
the  greatest  frequency,  with  the  possible  exception  of 
November.  The  average  difference  between  the  eve¬ 
ning  dew  point  and  the  ensuing  minimum  reaches  its 
maximum  in  May,  with  secondary  maxima  in  November 
and  January,  and  minima  of  practically  the  same  amount 
in  February,  August,  and  September.  In  February  in- 
vesions  are  infrequent,  although  of  large  range,  while 
August  and  September  have  rather  frequent  inversions, 
but  of  small  range. 

The  curve  (b),  showing  the  variation  at  the  home 
slope  stations  at  Altapass,  Ellijay,  and  Tryon,  has  its 


maximum  in  May,  with  secondary  maxima  in  January 
and  November,  the  latter  month  ranking  next  to  May. 
There  are  also  three  minima,  August,  December,  and 
February,  named  in  order  of  their  respective  values. 
This  curve  accentuates  the  effect  of  conditions  attending 
large  inversions  in  May  and  November,  on  the  one 
hand,  and  those  with  small  inversions  in  August,  on 
the  other.  While  on  the  slope  the  excess  in  minimum 
temperature  over  the  previous  evening  dew  point  aver¬ 
ages  more  than  8°  in  May,  the  depression  below  the 
dew  point  in  August  is  more  than  2°,  the  average  varia¬ 
tion  in  this  series  being  10.6°. 

As  shown  by  the  curve  (b),  the  minima  on  the  slope 
seem  to  be  much  higher  than  the  previous  evening  dew 
point,  especially  in  the  spring,  as  compared  with  the 
curve  (c),  based  upon  the  differences  for  the  home  valley- 
floor  stations.  Curve  (c)  conforms  roughly  with  that 
showing  the  variation  for  all  the  stations  combined,  (a), 
with  maxima  of  about  the  same  value  in  January,  April, 
and  December,  and  with  a  minimum  in  September  and 
a  secondary  minimum  in  February.  However,  all  these 


Fig.  76.— Average  monthly  difference  between  evening  dew  point  and  ensuing  mini¬ 
mum  temperature. 


averages  at  the  base  stations  show  the  minimum  below 
the  dew  point  with  differences  ranging  from  2.6°  in  April 
to  7.5°  in  September,  there  not  being  a  single  month  when 
ensuing  minimum  averages  above  the  previous  evening 
dew  point. 

Notwithstanding  the  difference  in  exposure  between 
individual  home  stations,  there  seems  to  be  considerable 
similarity  in  the  relations  existing  between  the  minimum 
and  the  dew  point  at  the  slope  stations,  on  the  one  iiand, 
and  at  the  valley  floor  stations,  on  the  other  hand,  as 
shown  by  curves  (b)  and  (c). 

The  above  results  are  in  harmony  with  the  thermal 
conditions  as  understood  in  mountain  regions.  At  sun¬ 
set,  the  time  when  the  dew-point  readings  are  taken,  the 
temperature  along  the  slope  is  fairly  uniform  from  the 
summit  to  the  base,  and  naturally  the  ensuing  minima  are 
relatively  low  on  the  valley  floors  and  high  on  the  slopes 
in  the  midst  of  the  thermal  belts.  These  variations,  of 
course,  are  exceedingly  large  on  individual  nights,  espe¬ 
cially  during  inversions,  and  it  should  be  apparent  that 
there  would  be  great  difficulty  in  determining  through 
the  use  of  formulas  with  any  refinement  the  ensuing 
minimum  temperature  in  this  mountain  region. 


30442-23- 


4 


92 


SUPPLEMENT  NO.  19. 


LENGTH  OF  GROWING  SEASON. 

The  length  of  the  growing  season  is  usually  determined 
on  the  basis  of  the  length  of  time  between  the  last  freeziug 
temperature  in  the  spring  and  the  first  freezing  tem¬ 
perature  in  autumn,  but  sometimes  also  from  the  dura¬ 
tion  of  the  mean  temperature  of  42.8°  or  above.  So  far 
as  the  first  plan  is  concerned,  it  is  generally  considered 
that  conditions  are  favorable  for  plant  growth  during 
any  period  when  the  minimum  temperature  does  not  fall 
below  32°,  and  the  second  plan  is,  in  fact,  based  upon  the 
first,  and  under  it  the  temperature  conditions  would  be 
much  the  same,  provided  the  daily  range  in  temperature 
at  the  place  under  consideration  averages  about  21°  or 
22°.  Thus,  if  the  minimum  temperature  were  32°  and 
the  maximum  53.6°,  the  mean  would  be  42.8°.  However, 
there  is  great  variation  in  the  range  in  temperature,  in 
some  parts  of  the  country  the  range  in  clear  weather 
exceeding  30°,  40°,  and  even  50°,  while  in  other  parts 
the  average  range  is  hardly  more  than  10°.  In  the  North 


temperature  in  the  spring,  the  earliest  date  of  freezing 
temperature  in  autumn,  and  the  four-year  average  of 
these  dates;  also  the  earliest  date  of  the  occurrence  of 
the  last  32°  in  the  spring  and  the  latest  occurrence  of  the 
first  32°  in  autumn,  together  with  the  length  in  days  of 
the  longest  and  shortest  growing  seasons,  as  well  as  the 
average  length  of  the  growing  season  for  the  period  of 
observations.  It  can  readily  be  seen  that  there  is  a  great 
variation  in  the  periods,  depending  largely  upon  altitude, 
the  more  elevated  groups  having  much  shorter  seasons 
than  those  nearer  sea  level.  The  valley-floor  stations 
have  the  shortest  seasons  of  tlieir  respective  groups  where 
valley-floor  stations  exist,  and  the  longest  periods  usually 
occur  on  the  slopes,  but  in  some  instances  at  the  summit. 

It  will  be  noted  by  examining  Table  34  that  often  the 
earliest  or  latest  occurrences  are  given  at  many  points  on 
the  same  date,  and  this  can  be  understood  when  it  is 
considered  that  the  specified  dates  do  not  indicate  any 
temperature  more  definite  than  the  reading  of  32°,  while, 


Fig.  77.— Length  of  growing  season. 


Carolina  mountain  region  the  daily  range  varies  consid¬ 
erably,  but  the  mean  for  all  the  research  stations  for  the 
four  years  is  21.3°,  so  that  a  minimum  of  32°  would,  on 
the  average,  closely  represent  a  mean  temperature  of 
42.8°. 

The  last  and  first  occurrences  of  freezing  temperature 
are  taken  as  the  limits  of  the  growing  season  in  this  review 
of  the  situation  in  the  North  Carolina  mountain  region. 
Data  based  upon  the  occurrences  of  actual  frost  are  not 
used,  because,  while  hoar  frost  is  frequently  observed  on 
the  valley  floors,  it  is  seldom  seen  on  the  slopes  except 
on  benches  and  in  coves.  There  is,  moreover,  no  instru¬ 
mental  record  of  frost  possible.  Therefore,  a  season 
based  upon  the  occurrences  of  actual  freezing  temperature 
is  preferred,  simply  because  minimum  temperature  data 
are  available  at  every  station  employed  in  the  research. 

The  average  of  the  growing  season  for  the  four  years 
of  the  research  does  not,  of  course,  represent  the  normal, 
as  the  period  is  entirely  too  short,  nevertheless  it  is 
important  that  it  be  stated.  The  summary  of  these  con¬ 
ditions  appear  in  Table  24,  the  latest  date  of  freezing 


as  a  matter  of  fact,  the  temperatures  at  some  points  on 
the  dates  in  question  were  several  degrees  lower,  and  when 
later  occurrences  of  freezing  temperatures  did  not  occur  at 
any  point  in  a  certain  season  on  the  given  slope,  stations 
having  normally  a  lower  temperature  appear  in  the 
table  as  having  just  as  long  a  growing  season. 

Figure  77  graphically  illustrates  the  lengths  of  the  grow¬ 
ing  season  by  the  heavy  black  lines,  and  in  Figure  78 
these  periods  are  shown  by  groups  and  elevations.  Tak¬ 
ing  the  groups  as  whole  (fig.  78)  the  most  elevated,  the 
Flat  Top  orchard  at  Blowing  Rock  and  the  Waldheim 
orchard  at  Highlands,  have  naturally  the  shortest  growing 
seasons,  and  Tryon,  the  group  nearest  sea  level,  the 
longest  growing  season,  the  extremes  ranging  from  an 
average  of  117  days  at  Highlands  No.  3  in  the  frost 
pocket  to  223  days  at  Tryon  No.  2  in  the  center  of  the 
thermal  belt,  with  a  difference  in  elevation  of  2,345  feet. 

Of  the  individual  groups,  station  No.  1,  where  located 
on  a  valley  floor,  has  in  every  instance  the  shortest  season 
except  at  Tryon.  There  the  season  is  slightly  shorter 
at  the  summit,  197  days  as  compared  with  200  at  the 


THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 


base  station,  and  this  is  due  to  the  cooling  effect  of  the 
great  mass  near  the  summit  and  the  influence  of  the 
mountain  breeze  on  the  floor,  which  often  raises  the 
temperature  at  No.  1  during  nights  of  inversion.  At 
Altapass,  also,  the  shortest  season  is  at  the  summit, 
because  of  the  surrounding  great  area,  but  here  we  have 
no  valley-floor  station  for  comparison,  as  No.  1  is  located 
on  the  slope.  In  the  Satulah  orchard  at  Highlands, 
where  stations  Nos.  1  and  2  are,  No.  1  has  a  longer  season 
than  No.  2  bv  eight  days.  However,  both  are  located 
on  a  slope  directly  under  Mount  Satulah,  and  the  more 
elevated  station  naturally  has  the  shorter  growing  season. 
These  are  the  only  lowest  level  stations  in  the  various 
groups  that  do  not  have  the  shorter  seasons. 

The  stations  on  the  short  slopes  having  the  longest 
seasons  are  almost  invariably  found  at  the  summit,  as 
at  Wilkesboro,  Bryson,  Blantyre,  Hendersonville,  and 
Transon,  including,  of  course,  the  Waldheim  orchard  at 
Highlands.  Mount  Airy  and  Asheville  seem  to  be  the 
only  exceptions  in  this  respect.  At  the  summit  of  Mount 
Airy  the  season  is  four  days  shorter  than  at  No.  2  on  the 
west  slope  and  but  three  days  longer  than  at  No.  3  at  the 
same  height  as  No.  2  on  the  east  slope,  while  at  Ashe¬ 
ville  the  variation  in  the  length  of  the  season  at  all  five 
stations  in  the  group  is  very  small,  the  range  being  only 
three  days.  In  fact,  this  is  the  smallest  difference  noted 
in  any  of  the  groups.  The  largest  range  is  in  the  Wald¬ 
heim  group  at  Highlands,  from  117  days  at  No.  3  to  168 
days  at  No.  5,  400  feet  above,  No.  1  in  the  Satulah 
orchard  at  the  same  place  averaging  187  days.  Here 
we  have  within  the  small  radius  between  the  base  stations 
in  the  two  orchards  a  difference  in  the  growing  season  of 
70  days,  and  this  is  principally  because  of  the  low  mini¬ 
mum  temperatures  at  No.  3,  so  often  referred  to  as  a 
frost  pocket. 

Gorge  is  the  only  long  slope  having  a  vertical  height  of 
1,000  feet  or  more  on  which  the  longest  season  is  found 
at  the  summit,,  or  at  least  close  to  it,  both  stations  Nos. 
4  and  5  having  the  same  number  of  growing  days,  201. 
Ellijay,  having  by  far  the  longest  slope,  1,760  feet  in 
vertical  height,  has  its  longest  season,  190  days,  at  station 
No.  3,  the  figures  there  shading  off  in  both  directions 
toward  the  base  and  the  summit,  with  167  and  185  days, 
respectively.  The  period  at  the  summit,  185  days,  seems 
unusually  long  considering  its  elevation,  4,000  feet,  and 
this  is  doubtless  because  of  the  small  surface  area  at  the 
upper  elevation,  the  temperature  there  partaking  largely 
of  the  free  air.  This  period  is  in  contrast  with  the  shorter 
period,  164  days,  at  the  No.  5  station  at  Blowing  Rock, 
located  at  about  the  same  elevation  above  sea-level,  but 
where  the  surrounding  surface  area  is  great. 

These  figures  show  the  decided  effects  of  inversions  m 
that  the  shortest  season  is  most  always  found  on  the 
valley  floor,  actual  freezing  temperature  being  more 
prevalent  there  than  at  the  higher  levels.  At  the  same 
time  effect  of  norm  conditions  is  apparent  in  the  fact 
that  the  longest  season  is  at  the  summit  of  no  long  slope, 
except  at  Gorge,  and  even  there  the  season  at  the  summit 
is  no  longer  than  at  station  No.  4,  the  one  next  below  on 

the  slope.  „  .  , 

Now,  viewing  the  length  of  the  season  for  the  vaiious 

stations  by  elevation  only,  as  shown  in  Figure  78,  we 
find  again  that  of  the  stations  having  approximately 
the  same  elevation  the  valley-floor  stations  in  every 
instance  have  the  shortest  season,  while  the  longest 
seasons  are  found  either  on  the  slope  or  at  the  summit. 
The  base  stations  located  on  valley  floors  where  the 
minimum  temperature  averages  especially  low  during 
nights  of  inversion  have  short  growing  seasons  as  com¬ 
pared  with  slope  stations  having  approximately  the 


same  elevation.  Thus,  Highlands  No.  3  has  a  much 
shorter  season  than  the  stations  on  the  slopes  and  even 
at  the  summits  in  other  groups.  As  stated  before,  the 
length  of  the  season  at  this  station,  having  an  elevation 
above  sea  level  of  3,670  feet,  is  only  117  days,  and  this 
is  in  strong  contrast  with  the  summit  station  at  Ellijay, 
about  15  miles  distant  and  having  an  elevation  of  4,000 
feet,  which  has  a  growing  season  of  185  days.  The  base 
station,  Blantyre  No.  1,  2,090  feet  above  sea  level,  a 
cold  station,  has  a  season  161  days  in  length,  shorter 
than  all  slope  and  summit  stations  having  the  same  or 
even  greater  elevation  and  24  days  shorter  than  the 
summit  station  at  Ellijay,  almost  2,000  feet  higher. 

It  would  be  important  if  the  exact  relation  between  the 
length  of  the  growing  season  and  the  elevation  could  be 
determined,  but  there  are  complications  that  prevent  a 
solution.  A  comparison  generally  throughout  the  region  is 
difficult  because  of  the  great  variation  in  the  topography. 

Moreover,  the  figures  in  Table  24  indicate  at  a  glance 
the  necessity  for  longer  records  to  determine  the  average 
length  of  the  growing  season.  For  instance,  at  High¬ 
lands  No.  3,  which  has  the  shortest  season,  117  days, 


Fig.  78.— Length  of  growing  season;  stations  grouped  according  to  elevation  above  sea 

level. 

within  the  four-year  period,  one  of  the  seasons,  1915, 
has  a  length  of  135  days,  while  another,  1913,  only  100 
days.  The  four-year  average  at  he  base  station  at 
Tryon  is  200  days,  and  the  range  during  that  period  is 
31  days,  one  season,  1915,  having  213  days,  and  another, 
1913,  only  182  days.  Again,  at  the  base  station  at  Cane 
River  there  is  a  range  during  the  four  years  of  39  days, 
and  this  is  exceeded  at  Blowing  Rock  Nos.  4  and  5  and  at 
Transon  No.  1,  where  the  range  amounts  to  55  days, 
the  greatest  of  all.  Hence  it  must  be  apparent  that  the 
average  for  the  four-year  period  only  can  not  be  con¬ 
sidered  without  qualification,  and  a  period  of  15  or  20 
years  is  necessary  in  order  to  establish  true  average  values. 

In  making  any  comparison  of  stations  in  different 
groups  due  allowance  has  to  be  made  for  difference  in 
fatitude,  and  in  this  connection  reference  should  be  made 
to  Mr.  P.  C.  Day’s  paper  12  which  indicates  that  tnere  is 
a  normal’ difference  of  about  15  days  in  the  growing  season 
between  the  northern  and  the  southern  boundaries  of 
western  North  Carolina.  Thus  normally,  Highlands, 
near  the  southern  border,  would  have  a  growing  season 
15  days  longer  than  places  near  the  northern  border 
having  the  same  elevation,  and  yet  the  coldest  station  at 

1*  Frost  Data  of  the  United  States,  Bulletin  V,  U.  S.  W  eather  Bureau. 

See  also  Atlas  of  American  Agric.,  frost  folio,  etc. 


94 


SUPPLEMENT  NO.  19. 


Blowing  Rock  No.  3,  has  an  average  growing  season  24 
days  longer  than  station  No.  3  at  Highlands  in  the  frost 
pocket,  although  there  is  only  about  100  feet  difference 
in  elevation.  However,  this  statement  does  not  mean  that 
Highlands,  as  a  whole,  is  a  cold  place,  but  has  reference 
only  to  the  special  conditions  at  the  base  of  the  Wald¬ 
heim  orchard.  The  slope  above  No.  3  has  a  much 
higher  average  temperature,  with  a  growing  season  50 
days  longer. 

So  far  as  latitude  is  concerned,  the  length  in  days  of 
the  growing  season  gradually  decreases  northward,  but 


this  decrease  is  offset  by  the  longer  day  and  the  larger 
amount  of  sunshine  during  the  summer  at  the  more 
northerly  points.  At  the  time  of  the  summer  solstice 
the  day  along  the  northern  border  of  this  country  is 
about  two  hours  longer  than  on  the  coast  of  the  Gulf  of 
Mexico,  while  at  intermediate  points  the  differences  are, 
of  course,  much  less,  aside  from  the  gradual  shortening 
of  day  on  both  sides  of  the  solstice.  For  instance,  the 
average  length  of  day  during  the  growing  season  in 
North  Carolina  is  approximately  30  minutes  shorter  than 
in  the  North  Atlantic  States. 


Table  24. — Length  of  growing  season. 


Principal  and  Slope  station ;  elevation  of  base  stations  above  mean  sea  level 

(feet). 


Altapass: 

No.  1  (base)  Elevation  2.230. 

No.  2,  SE . 

No.  3,  SE . 

No.  4,  SE . 

No.5,  Summit . 

Asheville: 

No.  1  (base)  elevation  2,445.. 

Wo.  2,  N . 

No.  2a,  S . 

No.  3,  N . 

No.  3a,  S . 

Blantyre: 

No.  1  (base)  elevation  2,090.. 

No.  2,  NW . 

No.  3,  NW . 

No.  4,  NW . 

Blowing  Rook: 

No.  1  (base)  elevation  3,130.. 

No.  2,  S . 

No.  3,  SE  (base) . 

No.  4,  SE . 

No.  5,  SE . 

Bryson: 

No.  1  (base)  elevation  1,800.. 

No.  2,  N . 

No.  2a,  S . 

No.  3,  summit . 

Cane  River: 

No.  1  (base)  elevation  2,650.. 

No.  2,  N . 

No.  3,  NE . 

No.  4,  summit . 

Ellijay: 

No.  1  (base)  elevation  2,240.. 

No.  2,  N . 

No.  3,  N . 

No.  4,  N . 

No.  5,  summit . 

Globe: 

No.  1  (base)  elevation  1,625.. 

No.  2,  E . 

No.  3,  summit . : . 

Gorge: 

No.  1  (base),  elevation  1,400. 

No.  2,  NE . . 

No.  3,  S . 

No.  4,  N  (old) . 

No.  4,  NE.  (new) . 

No.  5,  summit . 

Hendersonville: 

No.  1  (base),  elevation  2,200. 

No.  2,  E . !.... 

No.  3,  E . 

No.  4,  summit . 

Highlands: 

No.  1  (base),  elevation  3,350. 

No.  2,  SE . . 

No.  3,  SE . 

'  No.  4,  SE . 

No.  5,  SE . 

Mount  Airy: 

No.  1  (base),  elevation  1,340. 

No.  2,  W . 

No.  3,  E . 

No.  4,  summit . 

Transon: 

No.  1  (base),  elevation  2,970. 

No.  2,  W . . 

No.  3,  W . 

No.  4,  summit . 

Tryon: 

No  1  (base),  elevation  950.. . 

No.  2,  SE . 

No.  3,  SE . 

No.  4,  SE . 

Wilkesboro: 

No.  1  (base),  elevation  1,240. 

No.  2,  N . . 

No.  3,  N . 

No.  4,  W . 


Height 
of  slope 
stations 
above 
base 
(feet). 


250 

500 

750 

,000 


155 

155 

380 

380 


300 

450 

600 


450 

450 

625 

800 


385 

385 

570 


190 

400 

,100 


310 

620 

240 

760 


300 

,000 


290 

615 

840 

840 

,040 


450 

600 

750 


200 

325 

525 

725 


160 

160 

360 


150 

300 

450 


380 

570 

,110 


150 

350 

430 


Apr.  10 
Apr.  21 

,  ..do . 

. .  .do . 

Apr.  27 

Apr.  21 
Apr.  28 

...do . 

. .  .do . 

...do . 


May  20 
Apr.  21 

...do . 

...do . 


May  11 

...do . 

May  20 
May  11 
. .  .do . 


May  12 
Apr.  21 
Apr.  28 
Apr.  21 

May  20 
May  11 
Apr.  29 
,  ..do . 


Apr.  28 
Apr.  21 

...do . 

Apr.  28 
Apr.  27 

Apr.  22 
Apr.  11 
Apr.  21 

May  12 
May  11 

..  -do _ 

Apr.  21 

...do _ 

..  .do _ 


Apr.  30 
Apr.  28 

,  ..do _ 

...do _ 


...do _ 

...do _ 

June  14 
Apr.  29 
..  -do _ 


Apr.  21 
Apr.  10 
Apr.  21 
Apr.  10 

June  11 
May  11 

...do _ 

..  .do _ 

Apr.  27 
Apr.  10 

..  .do _ 

...do... . 

Apr.  22 
Apr.  11 
Apr.  10 
...do. ... 


Oct.  2 
Oct.  9 
Oet.  10 
Oct.  9 
...do . 


Oct.  2 
Oct.  9 

,  ..do . 

...do . 

...do . 


Sept.  22 

...do . 

Oct.  9 
...do . 


Oct.  1 
Oct.  9 
Sept.  20 
Sept.  22 
...do . 


Sept.  22 
Oct.  2 

..do . 

Oct.  9 

Sept.  23 
Oct.  2 

...do . 

Sept.  30 

Sept.  22 

Oct.  9 

...do . 

...do . 


Oct.  10 

...do . 

...do . 


Oct.  2 

...do _ 

...do _ 

Oct.  10 

..  .do _ 

..  .do _ 


Sept.  22 

...do. ... 
Oct.  9 

Oct.  10 
Sept.  22 
Sept.  21 
Sept.  22 


Oct.  10 

..  .do _ 

. . .do. . . . 
..  .do _ 

Sept.  20 
Oct.  2 
Oct.  1 
Oct.  9 

Oct.  21 

..  .do _ 

. .  .do.. . . 
Oct.  9 

Oct.  11 
Oct.  10 
.  .do. 
Oct.  20 


Apr.  8 
Apr.  12 

...do . 

Apr.  16 
...do . 


Apr.  14 
Apr.  16 

...do . 

...do . 

,  ..do - 


Apr.  30 
Apr.  16 
Apr.  12 
..do . 


Apr.  22 

...do . 

May  5 
Apr.  26 
...do . 


Apr.  28 
Apr.  11 
Apr.  16 
Apr.  8 

May  5 
Apr.  22 
Apr.  19 
Apr.  22 

Apr.  24 
Apr.  10 
Apr.  12 
Apr.  16 
Apr.  17 

Apr.  17 
Apr.  6 
Apr.  8 

Apr.  27 
Apr.  22 
Apr.  19 
Apr.  8 

...do _ 

..  .do _ 


Apr.  23 
Apr.  22 
Apr.  16 
..  .do _ 


..  .do _ 

...do. ... 
May  29 
Apr.  20 
Apr.  22 

Apr.  11 
Apr.  4 
Apr.  11 
Apr.  8 

May  17 
Apr.  22 
. . .do. . . . 
Apr.  19 

Apr.  16 
Mar.  30 

..  .do _ 

Apr.  6 

Apr.  15 
Apr.  6 

..  .do _ 

...do.  ... 


Oct.  15 
Oct.  26 
Oct.  20 
Oct.  25 
Oct.  19 

Oct.  15 
Oct.  20 

..  .do _ 

...do _ 

...so _ 


Oet.  8 
Oct.  7 
Oct.  17 
Oct.  20 

Oct.  14 
Oct.  17 
Sept.  23 
Oct.  7 
..do . 


Oct.  8 
Oct.  13 

..do . 

Oct.  20 

Oct.  6 
Oct.  14 

..do . 

..do . 


Oct.  8 

.  .do . 

Oct.  19 

..do . 

.  .do . 


Oct.  20 
Oct.  26 
Oct.  20 

Oct.  16 
Oct.  15 

..  .do _ 

Oct.  26 

,.  .do _ 

. .  .do _ 


Oct.  8 
..  .do. 
Oct.  12 
Oct.  20 


...do... . 
Oct.  12 
Sept.  23 
Oct.  3 
Oct.  7 

Oct.  18 
Oct.  26 

...do _ 

..  .do _ 

Sept.  23 
Oct.  14 
..  .do... . 
Oct.  17 

Nov.  2 
Nov.  8 
Nov.  5 
Oct.  20 

Oct.  18 
Oct.  24 
Oct.  26 
Nov.  5 


Apr.  4 

...do . 

, .  .do . 

...do . 

...do . 


Apr.  10 
Apr.  4 

...do . 

..do . 

..do . 


Apr.  19 
Apr.  10 
Apr.  4 
. .  .do . 


Apr.  10 

...dp . 

Apr.  18 
Apr.  15 
...do _ 


Apr.  19 
Mar.  29 

...do . 

Mar.  28 

Apr.  19 
Apr.  11 

...do . 

Apr.  13 

Apr.  18 
Apr.  6 
Apr.  4 

_ do.... 

...do . 


Apr.  10 
Mar.  28 
...do . 


Apr.  16 
Apr.  10 
Apr.  4 
Mar.  29 
Mar.  28 
..  .do _ 


Apr.  19 
Apr.  14 
Apr.  4 
..  .do _ 


...do _ 

...do. ... 
May  10 
Apr.  5 
Apr.  13 

Apr.  4 
Mar.  28 
Apr.  4 
Apr.  5 

Apr.  18 
Apr.  11 
Apr.  10 
Apr.  4 

Apr.  5 
Mar.  23 

.  .do _ 

Mar.  28 

Apr.  11 
Mar.  29 
..do. ... 
..do. ... 


Oct.  28 
Nov.  15 
Oct.  27 
Nov.  15 
Oct.  27 


...do. 

...do. 

...do. 

...do. 

..do. 


Oct.  28 
Oct.  27 

...do . 

.  .do . 


..do . 

...do . 

Sept.  27 
Oct.  27 
..do . 


Oct.  28 

..do . 

.  .do . 

..do . 


Oct.  27 

. .  .do . 

..do . 

...do . 


Oct.  28 

...do . 

Oct.  27 

...do _ 

_ do _ 


Oct.  28 
Nov.  15 
Oct.  27 

Oct.  28 

...do _ 

..  .do _ 

Nov.  15 
Nov.  16 
. .  -do _ 


Oct.  28 
Oct.  27 
..  -do. 
...do _ 


...do _ 

..  .do _ 

Sept.  26 
Oct.  27 
...do _ 

Oct.  28 
Nov.  15 

..  .do _ 

..  .do _ 

Sept.  27 
Oct.  27 
...do.... 
..  .do... . 

Nov.  16 
..  .do. 
Nov.  15 
Oct.  28 

...do...  . 
Nov.  8 
Nov.  15 
Nov.  16 


201 

219 

195 

219 

194 

200 

195 
195 

193 
195 

173 

189 

190 

194 

189 

189 

158 

189 

189 

190 
199 

199 
206 

173 

189 

189 

189 

190 
190 

193 

194 

189 

195 
219 
207 

190 
190 
190 

219 

220 
220 

190 

189 

194 

194 

194 

193 

135 

189 

189 

201 

219 

219 

219 

158 

189 

189 

189 

213 

232 

226 

207 

200 
212 
219 
226 


175 

188 

189 

175 

174 

175 

176 
176 
176 

176 

153 

154 
185 
188 

162 

162 

130 

134 

134 

133 
175 
157 
188 

134 
162 

174 

156 

148 

169 

188 

175 

177 

178 
189 
188 

157 
163 
163 
189 
189 
189 

153 

147 

147 

176 

175 

147 

100 

146 

146 

184 

189 

184 

189 

103 

162 

162 

162 

182 

207 

207 

188 

177 
189 
189 
201 


Date  of  last  freezing  temperature  in  spring  during  four-year  period. 

W  Date  of  first  freezing  temperature  in  autumn  during  four-year  period. 

(c)  Four-year  average  date  of  (a). 

(d)  Four-year  average  date  of  (b). 


190 

197 

191 

192 
186 

184 
187 
187 
187 

187 

161 

174 

188 
191 

175 
178 
141 
164 
164 

163 

185 
180 
195 

154 

175 

178 

175 

16 

181 

190 

186 

185 

186 
203 
195 

172 

176 

179 
201 
201 
201 

168 

169 

179 

187 

187 

179 

117 

166 

168 

190 

205 

198 
201 

129 

175 

175 

181 

200 

223 

220 

197 

186 

201 

203 

213 


(e)  Earliest  date  of  last  freezing  temperature  in  spring  during  four-year  period. 

(f)  Latest  date  of  first  freezing  in  autumn  during  four-year  period. 

(g)  Length  in  days  of  longest  growing  season,  or  interval  between  (a)  and  (b)  of  same  year 

(h)  Length  in  days  of  shortest  growing  season,  or  interval  between  (a)  and  (b)  of  same  year. 

(i)  Average  length  of  growing  season,  or  interval  between  (c)  and  (d). 


THERMAL  BELTS  AND  FRUIT  GROWING  IN 


NORTH  CAROLINA. 


95 


FRUIT  GROWING  IN  THE  CAROLINA  MOUNTAIN  REGION 
AND  PERCENTAGE  OF  CROPS,  1913-1916. 

Apples  and  peaches  are  the  principal  fruits  grown  in 
the  mountain  region,  apples  largely  predominating, 
ihe  peaches  are  generally  raised  successfully  at  tlie 
lower  elevations  ranging  from  1,000  to  2,000  feet,  as  at 
Mount  Airy,  Wilkesboro,  and  Tryon;  but  at  higher 
elevations  there  is  usually  considerable  danger  to  the 
buds  on  account  of  winter-killing  and  sprint  frosts 
and  at  an  altitude  of  3,000  feet  most  varieties  of° peaches 
seldom  reach  maturity.  Generally  speaking,  there  were 
good  crops  of  peaches  in  1914  and  1915,  but  even  in  the 
lower  levels  the  peach  harvest  was  only  poor  to  fair  in 
1913  and  1916,  the  damage  in  the  latter  year  beino-  due 
to  winter-killing. 

Apples  have  been  raised  successfully  at  the  lower  and 
middle  levels,  but  thus  far  no  satisfactory  crops  have 
been  grown  at  an  elevation  as  high  as  4,000  feet,  and 
3,500  feet  seems  to  be  the  limit,  especially  in  the  northern 
portion  of  the  area,.  Above  that  level  the  season  is  too 
short  and  insufficient  for  the  maturing  of  the  fruit, 
even  though  there  be  no  damage  from  winter-killing  or 
spring  frosts.  On  this  account,  apples  grown  in  the 
higher  levels,  with  the  exception  of  those  especially 
adapted  to  the  climate,  seldom  reach  full  size.  The 
winter  apple  of  the  higher  altitudes  becomes  the  fall 
apple  at  the  lower  levels,  though  its  shape  is  sometimes 
so  different  that  it  cannot  at  first  be  recognized.  At 
the  middle  levels  apple  growing,  because  of  the  later 
blooming  in  the  spring  and  the  comparative  hardiness 
of  the  fruit,  meets  with  much  greater  success  than  that 
of  peaches,  as  shown  by  the  seasons  of  1913  and  1916, 
when  the  peach  crop  at  those  levels  was  practically  a 
complete  failure,  although  there  was  generally  a  good 
crop  of  apples.  In  fact,  in  1916  Bryson  raised  a  full 
crop  of  apples.  Nevertheless,  there  is  danger  to  the 
apple  buds,  as  well  as  to  the  peach  buds,  in  the  winter 
and  spring  because  of  freezes  following  long  periods  of 
warm  growing  weather. 

Other  fruits  are  raised  in  the  region,  but  they  are  of 
little  consequence,  with  the  exception  of  grapes,  and 
these  find  the  conditions  best  adapted  to  their  develop¬ 
ment  in  the  lower  levels,  and  especially  in  the  Tryon 
area,  where  this  crop  during  the  four  years  of  the 
research  attained  large  proportions. 

In  the  upper  part  of  the  Waldheim  orchard  at  High¬ 
lands,  the  highest  point  at  which  observations  were 
made  during  the  period  of  the  research,  with  an  eleva¬ 
tion  above  sea  level  of  4,075  feet,  the  conditions  so  far 
as  the  HF°  and  the  length  of  the  growing  season  are 
concerned  (see  Table  25),  seems  to  be  exceptionally 
favorable  when  they  are  compared  with  the  conditions 
at  the  base  of  the  orchard,  500  feet  lower  down  in  the 
frost  pocket  at  station  No.  3,  because  the  higher  posi¬ 
tion  has  access  during  nights  of  inversion  to  a  relatively 
large  amount  of  free  warm  air  in  proportion  to  the  area 
of  radiating  surface  as  compared  with  the  lower  position. 

However,  taking  the  two  orchards  at  Highlands 
together,  ranging  from  an  elevation  of  3,350  feet  at  the 
base  of  the  Satulah  orchard  to  4,075  feet  at  the  top  of 
the  Waldheim  orchard,  the  fruit  crops  during  the  four 
years  of  the  research  were  very  small.  The  peach  crop 
can  be  considered  negligible.  The  apple  crop  averaged 
about  45  per  cent,  ranging  from  25  per  cent  in  1913  to 
65  per  cent  in  1915,  the  loss,  however,  not  being  entirely 
due  to  low  temperature,  but  in  some  cases  to  hail, 
especially  in  1913  and  1916. 

As  compared  with  Highlands  near  the  southern  border 
of  the  State,  the  China  and  Flat  Top  orchards  at  Blowing 


Rock,  another  high-level  place  located  far  to  the  north 
show  even  lower  temperature  conditions,  the  HF° 
bemg  greater  and  the  length  of  the  growing  season  less 
(table  25)  if  we  except  the  record  at  station  No.  3  at 
Highlands,  which  is  really  not  a  part  fo  the  Waldheim 
orchaid,  but  rather  immediately  below  it,  therefore  not 
representing  true  orchard  conditions.  The  percentage 
of  the  apple  crop  during  the  four  years  at  Blowing  Rock 
averaged  much  lower  even  than  at  Highlands,  and  this 
in  spite  of  the  fact  that  the  orchards  at  Blowing  Rock 
are  given  better  attention  through  personal  supervision 
of  the  manager.  Yet  the  average  crop  for  the  four  years 
was  only  35  per  cent,  and  in  1915  it  fell  to  as  low  as  5  per 
cent,  the  damage  being  partly  due  to  hail ;  but  low  temper¬ 
ature  was  the  principal  cause.  The  China  orchard  at 
Blowing  Rock,  in  which  stations  Nos.  1  and  2  are  located, 
ranging  in  elevation  from  3,130  feet  to  3,580  feet,  is 
much  better  situated  than  the  Ilat  Top  orchard,  where 
the  elevation  ranges  from  3,580  feet  to  3,930  feet,  as 
shown  by  the  figures  in  Table  25,  the  crop  in  the  latter 
often  being  almost  negligible.  Although  the  temper¬ 
ature  is  raised  occasionally  by  the  mountain  breeze 
during  nights  of  inversion  on  the  floor  of  the  Flat  Top 
orchard,  this  property,  as  a  whole,  is  cold.  Some  attempt 
has  been  made  to  raise  peaches  at  Blowing  Rock,  but  m 
practically  every  instance  the  buds  were  killed  in  the 
spring  by  hard  freezes. 

Moreover,  Transon,  also  located  far  to  the  north,  has 
been  referred  to  as  a  location  having  low  temperature 
because  of  its  position  on  an  elevated  plateau  reaching 
from  2,970  feet  above  sea  level  to  3,420  feet.  The  figures 
in  Table  25,  showing  the  number  of  HF°  and  the  length 
of  the  growing  season,  bear  out  this  statement.  Here  in 
1913  and  1915  the  apple  crop  was  a  complete  failure,  and 
only  in  1914  was  there  a  heavy  yield. 

Ellijay,  ranging  from  2,240  feet  to  4,000  feet  in  ele¬ 
vation,  another  of  the  high-level  places  and  one  which 
ranks  next  to  Highlands  in  elevation  so  far  as  the  position 
of  its  summit  station  is  concerned,  is  favored  with  the 
best  conditions  meteorologically  of  the  four  places,  as 
shown  by  the  figures  in  Table  25,  and  especially  on  its 
slope  from  stations  Nos.  2  and  4,  where  the  orchard  trees 
are  planted.  Nevertheless,  even  there  the  apple  crop 
during  the  four-year  period  did  not  average  more  than 
55  per  cent,  the  best  season  being  in  1916,  with  an  average 
of  95  per  cent,  while  in  1913  ana  1915  the  average  was  as 
low  as  25  per  cent.  In  1913  the  buds  were  killed  in  the 
freeze  of  March  27,  while  the  exact  dates  of  damage  in 
1915  could  not  be  determined.  Some  peaches  are  grown 
at  Ellijay  on  the  slope  in  the  vicinity  of  station  No.  3  at 
an  elevation  of  2,960  feet  above  sea  level.  A  fair  crop 
was  raised  there  in  1914  and  1915,  but  in  1913  and  1916 
the  crop  was  a  complete  failure,  in  1913  on  account  of 
the  freeze  of  March  27,  and  in  1916,  the  freezes  of  March 
16  and  April  9. 

In  the  orchard  at  Cane  River,  reaching  from  slightly 
above  the  base  station  No.  1,  2,650  feet,  up  the  slope  to 
approximately  3,100  feet  above  sea  level,  the  best  crop 
oi  apples  was  harvested  in  the  year  1914,  when  the  yield 
was  85  per  cent.  However,  while  the  weather  conditions 
in  1916  at  that  place  were  especially  favorable,  the  crop 
amounted  to  only  65  per  cent  because  of  the  failure 
of  the  owner  to  spray  the  trees  properly.  The  seasons 
of  1913  and  1915  were  well-nigh  complete  failures,  10 
per  cent  and  20  per  cent,  respectively,  in  the  former 
year  because  of  the  freeze  of  March  27-28,  while  in  the 
latter  year  the  dates  of  damage  could  not  be  determined. 

The  altitude  of  the  portion  of  the  slope  at  Altapass 
upon  which  fruit  trees  are  planted  varies  from  2,500  to 


96 


SUPPLEMENT  NO.  19. 


about  3,100  feet  above  sea  level.  A  new  apple  orchard 
was  planted  there  in  1911,  but  there  are  some  seedlings 
and  peach  trees  that  have  borne  fruit  intermittently. 
The  new  apple  trees  had  not  come  into  bearing  at  the 
time  of  the  close  of  the  research,  and  the  seedlings  and 

Eeach  trees  had  borne  fruit  rather  indifferently.  The 
est  year  for  apples  was  in  1914,  when  the  crop  amounted 
to  80  per  cent,  and  for  peaches  in  1915,  with  a  yield  of 
80  per  cent  also.  Practically  no  apples  or  peaches 
reached  maturity  in  1916,  and  in  1913  the  yield  of  both 
crops  was  low.  This  slope  is  rather  cold,  because  of  the 
large  surface  area  near  the  summit.  It  is  also  rather 
steep  and  suffers  considerably  from  washing  of  the  soil 
during  heavy  rains. 

In  the  Hendersonville  orchard,  which  ranges  in  eleva¬ 
tion  from  2,600  to  about  3,000  feet  above  sea  level,  the 
principal  crop  is  apples,  there  having  been  no  attempt 
made  to  raise  peaches.  There  was  no  yield  of  apples, 
even,  in  1913,  because  of  the  freeze  of  March  27-28, 
and  in  the  ensuing  three  years  the  yields  varied  from  20 
per  cent  to  50  per  cent.  The  damage  in  1914  was  due 
to  freezes  and  droughts  and  in  1916  to  the  severe  freeze 
of  February  14. 

In  the  orchard  at  Asheville,  which  is  on  a  northerly 
slope  ranging  from  2,450  to  2,835  feet  above  sea  level, 
apples  are  grown  chiefly,  but  these  crops  thus  far  have 
never  been  large.  The  yield  in  1913  was  only  5  per  cent; 
in  1914,  25  per  cent;  in  1915,  50  per  cent;  and  in  1916, 
55  per  cent.  The  damage  in  1913  was  caused  by  killing 
of  the  bud  in  the  freeze  of  March  27-28  following  a  period 
of  high  temperature.  Various  reasons  are  ascribed  for 
the  results  in  1914  and  1915,  while  in  1916  the  freeze 
of  April  9-10  and  of  March  16  were  the  principal  factors. 
The  upper  portion  of  this  orchard,  located  as  it  is  upon 
a  northerly  slope  with  heavy  timber  above  (see  fig.  18), 
suffers  from  too  much  shade.  The  owner  believed  that, 
for  some  reason,  there  was  deficient  pollination  in  that 
section,  and  he  tried  to  correct  it  through  the  use  of  bee 
swarms,  but  this  method  did  not  meet  with  success. 
As  a  matter  of  fact,  a  certain  amount  of  sunlight  is 
absolutely  necessary  for  the  growing  of  fruit,  aside  from 
the  fact  that  low  day  temperature  is  involved. 

Table  25  —Length  of  growing  season  and  number  of  hour-degrees  of 
frost  at  high-level  stations— Blov.ing  Rock,  Ellijay,  Highlands,  and 
Transon. 


Principal  and  slope  stations;  elevation  of  base  stations 
above  mean  sea  level  (feet). 


Height 
of  slope 
stations 
above 
base 
(feet). 


a 


Blowing  Rock: 

No.  1  (base),  elevation  3,130 

No.  2,  S . 

No.  3,  SE.  (base) . 

No.  4,  SE . 

No.  5,  SE . 

Ellijay: 

No.  1  (base),  elevation  2,240 

No.  2,  N . 

No.  3,  N . 

No.  4,  N . 

No.  5,  summit . 

Highlands: 

No.  1  (base),  elevation  3,350 

No.  2,  SE . .... 

No.  3,  SE.  (base) . 

No.  4,  SE . 

No.  5,  SE . 

Transon: 


450 

450 

625 

800 


310 

620 

1,240 

1,760 


200 

325 

525 

725 


No.  1  (base),  elevation  2,970 
No.  2,  W . 

No. 3,  w . 

No.  4.  summit. . 


150 

300 

450 


b 


175 

285 

178 

292 

141 

345 

164 

316 

164 

339 

167 

241 

181 

195 

190 

189 

186 

210 

185 

251 

187 

166 

179 

195 

117 

367 

166 

270 

168 

261 

129 

295 

175 

303 

175 

281 

181 

283 

(a)  Length  of  growing  season  in  days  based  upon  the  average  interval  between  the 
date  of  last  occurrence  of  32“  in  spring  and  the  first  occurrence  in  autumn  during  the 
period  from  1913-1916,  inclusive. 

(b)  Total  number  of  hour-degrees  of  frost  during  selected  periods  of  both  inversions 
and  norms. 


The  orchard  at  Blantyre  is  a  part  of  the  State  farm, 
and  it  therefore  has  received  more  attention  in  a  scien¬ 
tific  way  than  most  other  orchards  in  the  North  Carolina 
region.  Peaches  have  been  grown  on  that  property  in 
the  vicinity  of  the  base  station  at  an  elevation  of  2,100 
feet  above  sea  level,  but  the  yield  has  been  rather  indif¬ 
ferent,  although  an  excellent  crop  was  raised  in  1915, 
with  a  percentage  of  90.  The  yield  amounted  to  only 
5  per  cent  in  1916,  when  the  buds  were  winter-killed  by 
the  freeze  of  February  3  and  14.  The  apple  orchard  is 
situated  higher  up  on  the  northerly  slope  of  Little  Fod- 
derstack  at  an  elevation  ranging  from  2,400  to  2,700  feet 
above  sea  level.  There  was  no  yield  of  apples  whatever 
in  1913  because  of  the  freeze  of  March  27-28.  The  crop 
averaged  50  per  cent  in  1914  and  1916,  and  only  15  per 
cent  in  1915.  Blight  is  given  as  the  principal  reason  for 
the  low  yield  in  1915. 

In  the  orchard  at  Bryson,  which  is  located  far  to  the 
west  in  the  middle  levels  of  the  mountain  region,  with 
its  base  station  1,800  feet  above  sea  level,  there  were  ex¬ 
ceptionally  large  crops  of  both  apples  and  peaches  in 
1914  and  1916,  the  yield  of  both  being  practically  the 
maximum  possible  in  those  years.  Bryson  did  not  suf¬ 
fer  from  injury  in  1916  like  several  other  sections,  appar¬ 
ently  because  the  temperature  during  the  winter  was  more 
uniform.  There  was,  however,  some  damage  to  peaches 
on  April  10  of  that  year.  In  1913  the  apple  crop 
amounted  to  only  20  per  cent  on  account  of  the  severe 
freeze  of  March  27,  which  killed  nearly  all  of  the  buds, 
and  in  1915  there  was  a  fair  crop,  50  per  cent,  the 
deficiency  being  attributed  to  the  heavy  crop  of  the 
previous  year  rather  than  to  damage  from  weather 
conditions. 

Mount  Airy,  whose  base  station  is  1,340  feet  above 
sea  level,  located  in  the  eastern  foothills  of  the  mountain 
region  well  to  the  north,  seems  to  have  an  especially  favor¬ 
able  position  from  a  climatic  standpoint,  and  there 
apples  and  peaches  are  raised  with  equal  success  on  the 
slope  reaching  up  to  the  knob  360  feet.  The  average 
yield  during  the  four-year  period  was  70  per  cent  and 
75  per  cent,  respectively.  In  1913  there  was  some  damage 
from  hail  in  May  to  both  apples  and  peaches.  In  1915 
the  weather  conditions  were  excellent,  but  there  was 
damage  to  apples  by  twig  blight.  In  1916  the  peach 
crop  fell  to  its  lowest  point,  30  per  cent,  due  to  winter- 
killing  on  February  14. 

On  the  portion  of  the  slope  at  Tryon  ranging  from 
950  feet  above  sea  level  at  the  base  to  1,520  feet  at 
station  No.  3,  the  climatic  conditions  are  especially 
favorable  for  the  raising  of  fruit,  the  apple  crop  during 
the  four-year  period  averaging  80  per  cent  and  the  peach 
crop  70  per  cent.  Tryon  has  some  of  the  finest  vine¬ 
yards  in  the  country  at  an  elevation  of  250  to  600  feet 
above  the  valley  floor  and  approximately  1,150  to  1,500 
feet  above  sea  level.  The  vineyard  in  which  the  research 
stations  were  located  reported  practically  a  full  crop  of 
grapes  for  the  four  years,  averaging  99  per  cent.  The 
center  of  the  thermal  belt  on  the  Tryon  slope,  as  already 
states,  is  especially  low,  and  this  fact,  together  with  the 
southerly  location,  insures  most  highly  favorable  tem¬ 
perature  conditions  for  fruit  growth. 

The  weather  conditions  at  Wilkesboro  are  much  the 
same  as  at  Mount  Airy,  and  no  special  mention  of  the 
fruit  yield  there  need  be  made.  No  fruit  of  consequence 
has  ever  been  raised  at  either  Globe  or  Gorge  on  account 
of  the  rocky  formations  and  poor  soil  conditions.  The 
temperature  on  the  upper  half  of  the  Gorge  slope  is  as 
favorable  for  fruit  growing  as  any  in  the  Carolina  moun¬ 
tain  region,  but  it  has  been  most  difficult  to  clear  the 


THERMAL  BELTS  AND  FRUIT  GROWING  IN  NORTH  CAROLINA. 


ground  on  account  of  the  large  number  of  rocks  and 
bowlders. 

While  the  discussion  of  the  yields  in  the  foregoing 
paragraphs  in  the  various  orchards  where  research  sta¬ 
tions  were  maintained  has  mainly  to  do  with  weather 
conditions,  it  should  be  obvious  that  failures  may  in 
many  cases  be  charged  to  other  causes.  The  varying 
temperature,  of  course,  is  the  principal  factor  meteoro¬ 
logically  in  its  effect  upon  the  yield  of  fruit,  but  the 
question  of  precipitation  is  also  often  involved.  It  is 
seldom  that  droughts  occur  in  the  mountain  region,  but 
nevertheless  dropping  in  some  sections  has  been  ascribed 
to  drought,  especially  in  1913  and  1914  during  May. 
On  the  other  hand,  excessive  precipitation  is  frequently 
injurious  in  that  it  sometimes  prevents  necessary  spray¬ 
ing,  including  that  for  fungus  diseases.  Moreover,  ex¬ 
cessive  precipitation  invites  fungus  growth.  Hail,  too, 
often  causes  serious  damage,  especially  in  the  higher 
elevations  and  in  the  southern  portion  of  the  region. 

Moreover,  some  of  the  orchards  receive  far  better  care 
from  a  scientific  standpoint  than  others,  the  growers 
following  the  instructions  from  the  State  horticulturist 
and  the  Agricultural  Experiment  Station  more  or  less 
conscientiously.  The  percentages  of  average  yields, 
therefore,  do  not  necessarily  indicate  whether  the  meteoro¬ 
logical  conditions  were  favorable  or  unfavorable,  except 
in  a  general  way.  For  instance,  it  is  hardly  fair  to 
compare  from  a  meteorological  viewpoint  the  yield  of 
the  orchard  at  Mount  Airy,  which  receives  the  best  possi¬ 
ble  attention,  with  those  in  other  sections,  which  are 
more  or  less  neglected. 

The  conditions  shown  for  any  four-year  period,  of 
course,  are  not  necessarily  the  average  for  the  region, 
and  it  is  possible  that  over  a  long  term  of  years  greater 
average  success  would  be  attained  in  the  growing  of 
fruit  than  the  figures  in  this  publication  would  indicate. 
Moreover,  no  artificial  means  for  raising  the  temperature 
on  critical  nights  through  the  use  of  heaters  had  been 
tried,  nor  is  such  a  plan  practicable  because  of  the 
topography  of  the  region,  except  in  a  few  instances. 


FRUIT  GROWING  AT  HIGH  ELEVATIONS  IN  THE  WEST. 

Apparently  success  has  been  attained  in  the  raising 
of  fruit  at  much  higher  levels  in  the  West  than  in  the 
North  Carolina  mountain  region,  but  with  the  aid  of 
orchard  heaters.  Grand  Junction,  Colo.,  for .  instance, 
with  an  elevation  above  sea  level  of  4,667  feet,  is  a  fairly 
representative  area  in  the  subarid  fruit-growing  section. 
There  the  mean  annual  temperature  is  51.2°,  as  com¬ 
pared  with  55.1°  at  Asheville,  N.  C.,  at  a  much  lower 
elevation,  2,255  feet.  However,  the  mean  temperatures 
at  these  two  places  do  not  indicate  at  all  the  range  of  the 
extremes,  the  maxima  being  much  higher  at  Grand 
Junction  and  the  minima  much  lower  than  at  Asheville. 
For  instance,  in  the  four-year  period  of  this  research 
the  temperature  at  Grand  junction  ranged  from  a  max¬ 
imum  of  100°  to  a  minimum  of  —19°,  while  that  at 
Asheville  ranged  from  94°  to  4°  above  zero.  However,  the 
extremes,  whether  for  the  year  or  for  the  day,  are  main¬ 
tained  at  Asheville,  because  of  the  higher  vapor  pressure, 
for  a  longer  period  than  at  Grand  junction.  In  other 
words,  the  temperature  at  Asheville  may  continue  at 
its  highest  and  lowest  points  on  any  day  for  an  hour  or 
two  while  at  Grand  Junction  the  extremes  are  only 
momentary,  so  that  actual  maximum  and  minimum 
temperature  data,  for  instance,  do  not  by  any  means 
indicate  the  relative  number  of  hour-degrees  of  frost 
involved. 


CONCLUSION. 


It  should  be  apparent  from  the  data  presented  in  the 
discussion  that  minimum  temperature  and  its  duration 
are  the  chief  factors  involved  in  the  growing  of  fruit  in 
the  North  Carolina  mountain  region,  just  as  they  are  in 
any  other  orchard  region,  provided,  of  course,  sufficient 
moisture  is  supplied  through  rainfall  or  irrigation. 

However,  maximum  temperature  is  often  a  considera¬ 
tion.  It  has  been  shown  that  the  maxima  are  much 
higher  in  the  winter  on  a  southerly  than  on  a  northerly 
slope  and  in  all  seasons  of  the  year  higher  on  a 
westerly  than  on  an  easterly  slope.  But  relatively  high 
maximum  temperatures  are  not  always  to  be  desired. 
Where  the  maximum  is  abnormally  high  in  the  winter 
and  spring,  so  as  to  force  the  buds  prematurely,  there  is 
danger  of  damage  from  ensuing  frosts  or  freezes,  some¬ 
times  in  contrast  with  slopes  where  the  maximum  does 
not  rise  so  high.  In  any  case,  shade  must  be  avoided, 
such  as  noted  in  the  upper  portions  of  the  orchards  at 
both  Asheville  and  Cane  River,  because  it  not  only  pre¬ 
vents  necessary  sunlight,  but  also  serves  to  reduce  the 
sensible  temperature  after  precipitation  to  a  lower  point 
than  that  shown  by  the  thermometer  through  the  reten¬ 
tion  of  the  moisture  on  the  vegetation  and  fruit. 

So  far  as  the  minima  are  concerned,  it  is  obvious  that 
great  care  should  be  taken  in  the  selection  of  a  site  for 
an  orchard.  Valley  floors  must  in  nearly  all  cases  be 
avoided.  There  the  temperature  on  critical  nights  of 
inversion  often  falls  15°  or  20°,  and  sometimes  even  25° 
or  30°,  lower  than  higher  up  on  the  slope. 

vSome  valley  floors  are,  moreover,  colder  than  others! 
Wide  floors,  such  as  those  at  Blantyre  and  Bryson,  sur¬ 
rounded  by  high  mountains  at  some  little  distance,  where 
the  loss  of  heat  through  radiation  is  quite  rapid,  are  some¬ 
what  colder  than  other  floors  closely  shut  in,  such  as  at 
Ellijay.  The  latter  is  not,  indeed,  warm,  but  its  slightly 
higher  minima  as  compared  with  Blantyre  and  Bryson 
are  due  to  obstructed  radiation,  although  the  area  of 
radiating  surface  in  the  immediate  vicinity  of  the  closed- 
in  floor  is  unusually  large,  but  not  sufficient  to  offset  the 
obstruction  referred  to  by  raising  the  sky  line. 

Valley  floors  similar  to  those  at  Try  on  and  in  the  Flat 
Top  orchard  at  Blowing  Rock  have  been  shown  to  be 
warm  on  certain  nights  of  inversion  considering  their  ele¬ 
vation  above  sea-level,  both  relatively  warmer  than 
Ellijay,  and  this,  too,  in  spite  of  the  fact  that  the  floor 
at  Tryon,  especially,  is  wide.  However,  the  higher  aver¬ 
age  minima  at  Tryon,  as  well  as  Blowing  Rock,  are  due 
to  the  prevalence  of  the  nocturnal  mountain  breeze  down 
the  slope  and  valley  from  the  great  surface  area  around 
the  summer  station.  During  nights  of  inversion,  when 
conditions  are  not  favorable  for  the  mountain  breeze,  the 
temperature  falls  at  these  two  places  comparatively  low. 

While  the  great  area  above  is  responsible  for  the  noc¬ 
turnal  breeze  and  the  raising  of  the  minima  on  the  floor, 
it,  at  the  same  time,  causes  low  temperature  at  the  higher 
levels,  because  of  the  large  area  of  radiating  surface  in 
proportion  to  the  air  available  for  interchange,  so  that 
on  such  slopes  as  these  two,  as  well  as  at  Altapass,  the 
upper  levels  are  cold  and  the  valley  floors  often  compara¬ 
tively  warm.  .  .  , 

This  research  has  shown  that  the  mountain  breeze 
does  not  develop  at  night  and  flow  down  a  valley  unless 
there  is  great  surface  area  around  the  summit  station. 
On  no  valley  floor  where  the  slopes  culminate  m  knobs 
has  the  nocturnal  breeze  been  noted.  The  thermograph 
traces  on  the  floors  at  Bryson,  Blantyre,  Ellijay,  Gorge, 
Cane  River,  and  Mount  Airy,  all  with  small  mass,  never 


98 


SUPPLEMENT  NO.  19. 


show  any  sign  of  the  mountain  breeze.  Before  such  a 
breeze  develops,  there  must  be  available  a  relatively  large 
amount  of  heavier  and  potentially  colder  air  above.  And 
this  can  only  occur  over  a  plateau-like  surface.  There  is  no 
opportunity  for  such  development  over  a  knob.  Where  the 
highest  points  are  mere  peaks  or  knobs,  they  partake  of 
the  temperature  of  the  free  air  surrounding  and  are 
always  relatively  warm  on  nights  of  inversion,  and  this, 
too,  in  spite  of  the  fact  that  a  knob  is  best  situated  topo¬ 
graphically  for  loss  of  heat  through  radiation,  as  its  angle 
of  free  radiation  may  exceed  even  180°. 

The  descending  nocturnal  breeze  may  properly  be 
compared  with  a  waterlike  flow  as  it  passes  down  the 
slope  and  mixes  with  the  cold  air  of  the.  valley  floor,  and 
it  is  entirely  unlike  the  slow  exchange  of  free  air  over  a 
valley  with  that  resting  on  a  slope.  The  cold  air  some¬ 
times  collects  on  benches  or  coves  on  a  slope,  and  when 
great  difference  in  density  exists  between  it  and  the 
neighboring  free  air  the  cold  air  slips  off  and  passes  down 
the  slope,  immediately  giving  place  in  turn  to  warmer 
air.  Such  a  phenomenon  has  often  been  observed  at 
Blantyre  on  the  descending  slope  near  the  base  of  little 
Fodderstack. 

Coves  and  even  shelves  or  benches  on  slopes  should  be 
avoided  so  far  as  practicable  in  the  planting  of  fruit 
trees  because  of  the  low  night  minima,  making  possible 
the  formation  of  frost  there,  while  other  portions  of  the 
slope  entirely  escape. 

Many  topographical  conditions  are  involved  in  their 
effect  upon  the  minima  on  a  slope.  "(^Generally  speaking, 
the  steeper  the  slope  the  warmer  it  is  during  nights  of 
inversion^)  At  the  same  time,  if  there  is  a  steep  slope 
directly  opposite  and  close  by,  making  the  valley  deep 
and  narrow,  the  entire  slope  will  be  relatively  cold, 
rather  than  warm,  up  to  the  level  where  the  free  air 
becomes  practically  limitless,  although,  as  already 
stated,  its  base  may  be  warmer  than  a  wide  valley  floor. 
If  this  steep  slope  has  no  opposing  slope  and  it  culminates 
in  a  knob  above,  it  will  be  relatively  warm  its  entire 
length.  A  gradual  slope  is  naturally  colder  than  a 
steep  one,  and  the  nearer  it  approaches  to  the  level  of  a 
plain  the  colder  it  is. 

On  a  short  slope  culminating  in  a  knob  no  more  than 
500  feet  in  elevation  the  height  being  insufficient  to 
cause  more  than  a  degree  or  two  difference  in  tempera¬ 
ture  between  valley  floor  and  summit  on  nights  of  norm 
conditions,  such  as  Blantyre,  Bryson,  and  Mount  Airy, 
the  summit  is  the  safest  section  for  fruit  growing,  because 
during  nights  of  inversion  the  highest  minima  are  practi¬ 
cally  always  registered  at  that  level.  This  usually  is  the 
case  on  slopes  even  up  to  levels  as  high  as  1,000  feet 
above  the  valley  floor,  as  Gorge  and  Cane  River.  It  has 
been  shown  that  the  center  of  the  thermal  belt  on  some 
nights  of  inversion  is  even  as  high  as  the  summit  of 
Ellijay,  1,760  feet  above  the  valley  floor,  and  on  the 
average  the  thermal  belt  is  centered  more  than  1,200  feet 
above  that  floor,  due  to  the  fact  that  the  portion  of  the 
slope  lower  down  is  comparatively  cold.  However,  there 


is  always  greater  danger  from  top  freeze  at  the  higher 
elevations  of  long  slopes,  and  these  at  Ellijay,  for  instance, 
have  a  greater  number  of  H  F°  on  the  average  than  the 
level  of  600  or  700  feet  above  the  floor.  Usually  on  a 
slope  having  an  elevation  of  1,000  feet  or  more  above  its 
floor  the  safest  level,  from  the  standpoint  of  the  number 
of  II  F°  from  inversion  and  norm  conditions  combined, 
is  from  300  to  700  feet,  but  on  slopes  having  a  very  small 
grade  and  terminating  in  a  knob,  as  Gorge,  the  safest 
point  is  at  the  very  summit. 

Moreover,  if  the  summit  at  Ellijay  were  immediately 
surrounded  by  great  surface  area  at  that  level,  as  at  Tryon 
and  Altapass,  instead  of  being  on  a  mere  knob,  it  would 
be  much  colder,  and  this  would  serve  to  reduce  the  temper¬ 
ature  generally  over  its  upper  levels,  so  that  the  level  of 
the  thermal  belt  would  be  correspondingly  lowered  and 
its  width  reduced  to  very  small  limits.  Such  a  slope 
would  indeed  be  a  cold  one  practically  from  base  to  sum¬ 
mit,  if  there  were  high  opposing  slopes  close  by. 

While  the  slopes  at  Bryson  and  Blantyre  are  warm  as 
compared  with  their  respective  floors  during  nights  of 
inversion,  the}7  are,  nevertheless,  relatively  cold  for  their 
elevation,  because  they  are  located  in  vast  frost  pockets 
formed  by  surrounding  mountains  which  tower  above  at 
considerable  elevation.  Frost  pockets  must  be  avoided 
as  far  as  practicable,  whether  large  or  small.  The  one 
in  the  Waldheim  orchard  at  Highlands,  a  small  depres¬ 
sion  or  sink,  although  much  unlike  those  at  Bryson  and 
Blantyre,  is  nevertheless  equally  objectionable. 

An  ideal  slope  for  fruit  growing  is  one  of  moderate 
elevation  above  sea  level,  the  basic  altitude  varying,  of 
course,  in  different  portions  of  the  country,  fairly  steep 
and  culminating  in  a  knob  with  no  surrounding  moun¬ 
tains,  or  if  any,  at  least,  situated  so  far  distant  as  to  have 
no  effect  upon  the  temperature  conditions  of  the  slopes 
involved,  such  as  Mount  Airy  and  Wilkesboro,  or  the 
lower  levels  of  a  slope  such  as  Tryon,  which  is  warm  be¬ 
cause  of  the  absence  of  opposing  slope  and  because  of  the 
influence  of  the  nocturnal  breeze,  although  its  upper 
levels  are  cold  on  account  of  the  great  area  surrounding 
the  summit. 

The  subject  of  vegetation  must  be  considered,  dense 
vegetation  being  responsible  for  great  loss  of  heat  through 
radiation,  and  a  cultivated  orchard  is  therefore  warmer 
than  one  planted  in  grass. 

The  data  presented  in  this  study  make  plain  the  neces¬ 
sity  for  great  care  in  the  selection  of  a  property  for  the 
purpose  of  fruit  growing.  The  topography  of  a  region  is 
aramount.  Frost  pockets  should  be  avoided  and  valley 
oors  of  all  kinds  as  far  as  practicable,  unless  means  are 
available  for  orchard  heating.  The  altitude  above  sea 
level  is  in  every  case  a  consideration  and,  in  a  degree,  the 
elevation  above  the  valley  floor. 

All  these  questions  must  be  given  careful  consideration 
and  the  effect  of  one  upon  another  weighed  in  the  balance. 
No  hard  and  fast  rule  can  be  made  in  the  determination, 
as  the  factors  involved  are  so  many  and  so  complicated 
that  each  site  must  be  considered  by  itself. 


99 


THERMAL  BELTS  FROM  THE 


HORTICULTURAL  VIEWPOINT. 


APPENDIX. 


THERMAL  BELTS  FROM  THE  HORTICULTURAL  VIEW¬ 
POINT. 

By  W.  N.  Htjtt,  Former  State  Horticulturist. 

It  would  be  impossible  to  be  associated  in  any  capacity 
with  the  growing  of  fruit  in  North  Carolina  and  not  hear 
of  thermal  belts  or  cc verdant  zones.”  These  eupho- 
nious  terms  (whatever  they  may  mean)  are  more  or  less 
common  and  usual  expressions  found  daily  in  the  speech 
of  the  fruit  producers  of  this  State.  The  outsider,  on 
coming  in  contact  with  North  Carolina  fruit  growers,  is 
soon  led  to  inquire,  “What  are  these  belts  or  zones?” 
“Where  are  they  to  be  found?”  “What  are  their  char¬ 
acteristics  ?  ”  “Are  they  found  in  North  Carolina  alone  ?  ” 

Do  not  other  States  have  them?”  This  was  my  expe¬ 
rience  when,  in  1906,  I  came  to  North  Carolina  to  begin 
my  work  as  State  Horticulturist.  Previous  to  that  time 
I  had  been  closely  associated  with  the  fruit  growers  of 
other  States,  but  I  am  frank  to  admit  that  until  my 
coming  here  I  had  never  heard  of  a  thermal  belt  or  of  a 
verdant  zone.  But  the  fact  remained  that  such  belts  or 
zones  were  mentioned  frequently  by  the  North  Carolina 
fruit  growers,  and  the  practical  value  of  these  zones 
seemed  to  be  in  evidence,  for  a  grower  was  considered 
very  fortunate  if  he  owned  one  or  came  even  partially 
under  its  benign  influence. 

The  practical  men  who  make  their  living  from  mother 
earth  in  fruits,  vegetables,  grains,  or  other  products  are 
close  observers  of  nature  and  her  laws.  They  may  not 
always  be  able  to  correctly  interpret  her  ways  and  define 
her  laws,  but  if  they  have  observed  any  phenomenon 
and  formulated  any  practice  from  it  you  may  be  pretty 
sure  there  is  something  in  it,  and  you  will  be  unwise  if 
you  disregard  it  without  investigation.  As  a  horticul¬ 
tural  investigator  in  North  Carolina  I  felt  it  was  my 
duty  to  investigate  these  thermal  belts  and  verdant  zones. 

To  get  what  definite  data  I  could — not  just  hearsay — 
on  which  to  base  my  researches,  I  made  a  study  of  all 
available  published  literature  on  the  subject,  and  notes 
therefrom  appear  in  small  print  at  the  bottom  of  these 
pages.  In  making  my  trips  over  the  State  and  in  coming 
in  contact  with  fruit  growers  I  kept  up  a  constant  quest 
for  the  elusive  thermal  belt,  but,  like  an  ignis  fatuus, 
light  and  tenuous  as  air,  it  always  seemed  to  elude  my 
grasp.  One  thing,  however,  that  seemed  to  stand  out 
clearly  was  that  this  will-o’-the-wisp  was  the  tutelary 
deity  of  the  mountains,  less  seldom  seen  in  the  hills  and 
never  showing  its  form  in  the  plains. 

Here  seemed  to  be  some  explanation  why  North  Caro¬ 
lina  has  a  monopoly  of  thermal  belts:  One-third  of  its 
area  is  made  up  of  rolling  piedmont  hills  stretching  up  to 
another  third,  containing  the  highest  elevations  east  of 
the  Rocky  Mountains. 

My  work  as  State  Horticulturist  kept  me  in  contact 
with  the  growers  and  constantly  traveling  among  the 
orchards  at  all  seasons  of  the  year.  I  kept  careful  notes 
and  found  that  there  were  peculiar,  unaccountable  differ¬ 
ences  in  the  size  of  the  fruit  crops  from  various  localities, 
and  even  in  the  same  orchards,  where  climatic  conditions 
should  have  been  about  the  same.  A  wide  variation  in 
fruitage  was  often  found  in  the  same  varieties.  Some¬ 
times  in  a  year  when  weather  conditions  were  so  unfavor¬ 
able  all  over  the  State  that  it  would  seem  impossible  that 
any  fruit  would  survive  some  section,  or  some  orchards 
in  a  section,  would  bear  a  phenominal  crop  of  fruit.  A 
notable  case  of  this  kind  was  in  the  year  1907,  the  year  of 
the  Jamestown  Exhibition.  We  wished  to  make  there  a 


display  of  North  Carolina  fruit  throughout  the  whole 
season.  Ike  spring  of  1907  was  one  of  the  most  unfa¬ 
vorable  in  years,  and  it  looked  as  if  our  exhibition  project 
would  have  to  be  abandoned.  However,  it  was  found 
later  that  there  was  a  good  crop  of  fruit  in  most  of  the 
hillside  orchards  m  the  Brushy  Mountains  in  Wilkes  and 
Alexander  counties.  This  and  other  peculiar  phenomena 
that  had  been  noted  throughout  the  orchards  of  the 
mountain  regions  of  North  Carolina  for  four  or  five  years 
induced  me  to  undertake  a  definite  investigation  of  this 
subject. 

In  1907,  through  the  State  Board  of  Agriculture,  a 
branch  experiment  station  was  located  at  Blantyre  m 
Transylvania  County,  N.  C.,  at  an  altitude  of  2,100  feet. 
The  land  on  this  place  sloped  from  river  bottom  directly 
up  to  the  top  of  the  Little  Fodderstock,  including  one 
whole  side  of  the  mountain.  Though  some  of  this  land 
was  steep  and  in  places  rocky,  we  had  it  cleared  and 
planted  in  apples  and  peaches,  so  that  observations  could 
be  made  on  orchard  conditions  over  a  wide  range  of  slope 
and  altitude. 

In  1911  I  had  self-recording  instruments  (hydgother- 
mographs)  placed  at  the  different  stations  in  the  orchard— 
at  the  base,  midway  of  the  slope,  and  at  the  top  of  the 
orchard.  The  trace-sheet  records  of  these  instruments 
showed  a  wide  variation  in  temperature  during  the  24 
hours  between  these  different  stations,  sometimes  as 
much  as  10°.  This  looked  very  encouraging,  for  a  differ¬ 
ence  of  1°  or  2°  of  frost  at  blooming  time  will  make  all 
the  difference  between  success  and  failure  of  a  fruit  crop. 
How  comforting  it  would  be  to  a  fruit  grower  to  know 
that  his  orchard  or  part  of  it  was  in  a  thermal  belt  with 
8°  or  10°  higher  temperature. 

From  these  early  observations  we  learned  the  most 
constant  characteristic  of  thermal  belts — namely,  their 
variability.  Under  one  set  of  weather  conditions  we 
would  find  the  warmest  place  in  the  orchard  to  be  at  the 
bottom  of  the  slope;  under  another  set  of  conditions  at  the 
top,  and  now  again  at  the  middle  station. 

After  two  seasons  of  observations  with  those  three 
instruments  in  this  one  orchard  we  found  it  impossible 
to  arrive  at  any  definite  conclusions  unless  we  could 
check  and  compare  our  results  with  instruments  in  other 
orchards  at  different  altitudes  and  on  different  slopes. 
This  would  necessitate  the  installation  of  scores  of  very 
expensive  instruments  in  a  number  of  orchards  at  differ¬ 
ent  points.  To  get  anything  like  accurate  records, 
trained  and  paid  observers  would  be  necessary,  and  the 
recording  of  data  would  need  to  be  carried  on  for  a  num¬ 
ber  of  years.  From  this  it  was  seen  that  the  problem 
was  much  too  elaborate  and  comprehensive  to  be  handled 
with  the  facilities  and  finances  then  at  the  disposal  of  our 
experiment  station,  especially  when  the  more  simple 
and  practical  problems  of  horticulture  were  daily  de¬ 
manding  attention. 

In  discussing  these  problems  one  day  with  Mr.  L.  A. 
Denson,  Section  Director  for  North  Carolina,  he  sug¬ 
gested  that  we  lay  the  matter  before  the  Chief  of  the 
United  States  Weather  Bureau  at  Washington.  Con¬ 
sequently  we  both  made  a  trip  to  Washington  and  dis¬ 
cussed  the  whole  matter  with  Mr.  Willis  L.  Moore,  then 
Chief  of  the  Weather  Bureau.  Mr.  Moore  was  very 
much  interested  in  the  project  and  later  secured  the 
funds  for  carrying  on  the  investigation  on  an  extensive 
scale  with  the  necessary  instruments  and  paid  observers 
at  each  orchard  station.  Prof.  H.  J.  Cox,  of  the  Chicago 
office  of  the  Weather  Bureau,  was  appointed  to  take 


100 


SUPPLEMENT  NO.  19. 


charge  of  the  meteorological  side  of  the  work.  In  July, 
1911,  a  preliminary  survey  of  the  orchard  region  of 
western  North  Carolina  was  made  by  Professor  Cox,  Mr. 
Denson,  and  the  writer  and  orchards  selected  for  some  of 
the  stations.  Later  in  the  season,  the  selected  orchards 
were  surveyed  and  the  adjoining  territory  mapped  by 
F.  R.  Baker,  engineer  of  the  State  Department  of  Agri¬ 
culture.  Mr.  Baker  also  made  exact  altitude  determina¬ 
tions  for  the  instrument  recording  stations.  After  this 
was  done  Mr.  Denson  put  up  the  shelters,  installed  the 
instruments,  and  trained  the  observers  in  looking  after 
the  instruments  and  in  recording  other  data. 

In  August,  1912,  an  inspection  trip  of  these  orchard 
recording  stations  was  made  by  Professor  Cox,  Mr.  Denson, 


and  myself  and  additional  stations  selected  that  would 
seem  to  cover  conditions  not  already  met.  These  addi¬ 
tional  stations  were  mapped  and  instruments  installed 
in  them,  as  described  above. 

By  January  1,  1913,  practically  all  the  16  stations, 
as  shown  in  the  tables  that  follow,  were  located,  mapped 
and  the  observers  conversant  with  the  proper  handling 
of  the  instruments.  With  orchard  altitudes  ranging 
from  956  to  4,067  feet  and  with  every  possible  slope  and 
declivity,  if  there  is  any  such  thing  as  a  thermal  belt  it 
ought  to  be  found  and  located  in  this  range  of  varied 
territory. 

The  table  below  gives  the  accumulated  horticultural 
data  for  the  year  1913. 


Table  1. — Summary  of  horticultural  data  for  season  of  1913. 


Apples. 


Location. 

First 

bloom. 

Full 

bloom. 

Bloom 
all  shed. 

Dura¬ 
tion  of 
bloom. 

Days. 

Altapass . 

Apr.  20 

Apr.  29 

May  7 

17 

Asheville . 

Apr.  16 

May  1 

May  10 

24 

Blantyre . 

Apr.  21 

Apr.  28 

May  6 

13 

Blowing  Rock.... 

May  1 

May  8 

May  15 

15 

Bryson  City . 

Cane  River . 

Apr.  15 

Apr.  26 

May  7 

22 

Ellijay . 

Apr.  17 

Apr.  20 

May  4 

27 

Globe . 

Apr.  12 

Apr.  22 

May  2 

20 

Gorge . 

Apr.  25 

May  1 

May  7 

12 

Hendersonville. . . 

Highlands . 

Apr.  19 

May  1 

May  16 

27 

Mount  Airy . 

Apr.  10 

Apr.  15 

Apr.  20 

10 

Transon . 

Try on . 

Waynesville . 

Apr.  26 

May  5 

May  15 

19 

Wilkesboro . 

Apr.  27 

May  10 

...do. .. 

18 

Character  of 
bloom. 


Light . 

Very  light. 


Light . 

Heavy . 

/Extremely 
l  light. 

Light  on  up¬ 
per  slope; 
average 
lower. 


Light . 


Very  light. 

Light _ 

/Practically  \ 
\  no  bloom.  / 

Heavy . . . 
Average. 


Average. 
Light 
Heavy. .. 


Peaches. 


First 

bloom. 


}- 


Full 

bloom. 


Mar.  28  Apr.  3 


Bloom 

all 

shed 


Dura¬ 
tion  of 
bloom. 


rh  ,  Cause  of 
acterof  iniury- 
bloom. 


Freeze . . . 

{Killed  in 
bud  by 
high,  cold 
wind. 

Freeze . . 
Frost . . . 


Date  of 
injury. 


jner. 

(Mar. 


Killed  in 
bud  by 
high,  cold 
wind. 

.  Top  freeze. 

(Killed  in 
J  bud  by 
'  |  high,  cold 
\  wind. 

.  Cold  wind. 


.do. .. 


/Killed 
\  bud. 


Frost . . . 
Dry  weather 

Cold  w  ind . 
. do.. 


28... 

11... 

27-28 

28... 

24.. . 

12.. . 


May  10-11 
Mar.  27.. 


(Mar. 

1^ 


27.. . 

28.. . 
11-12 


Mar.  27-28 


{&• 

{*£ 

j-Mar.  27-28 


28... 

11-12 

28... 

11-12 


May  11-12 


Loss  by 
May 
drop. 


Per  ct. 
}  25 

Small. 


60 

25 

Light 


Very 

light- 


Heavy- 


25 


.  70 
None. 


[Mar.  27...  1 
(Apr.  28.. .1 
[May  11 _ J 

May 


27.. 

28.. 
11.. 

11 


10 


Yield  of 
apples. 


Per  cent. 
20 


Very  small. 
25 

20 

}  10 

25 

20 

25 

(») 

25 

Heavy. 

(’) 

65 

25 

45 


Yield  of 
peaches. 


Alti¬ 

tude. 


Per  ct. 


Feet. 

: 12, 230- 
\3, 230 

72,445- 
\2, 825 

;/2, 090- 
'  \2, 690 

73, 130- 
■\3, 930 

|/1, 800- 
12, 370 


Range 
of  alti¬ 
tude. 


Feet. 

}  1,000 


72, 650- 
•  ,13,750 


30 


/2, 240- 
\4,  000 

1,625- 
2, 625 
1,400- 
2,  440 
12, 200- 
, \2, 950 
/3, 360- 
14, 075 
/1,340- 
1  \1, 700 
2, 970- 
3, 420 
950- 
2, 060 


} 


380 

600 

800 

570 


}  1,100 

j  1,760 

1,000 
1,040 
}  750 

725 
360 
450 
}  1, 100 


I 


(1,240-1 
11,670  !/ 


430 


Almost  complete  failure. 


From  this  it  will  be  seen  that  the  time  of  first  bloom 
covered  a  period  of  24  days  from  April  7  at  Ellijay  to 
May  1  at  Blowing  Rock.  The  time  01  full  bloom  covered 
25  days  from  April  15  at  Mount  Airy  to  May  10  at 
Wilkesboro.  The  entire  range  of  bloom  over  the  whole 
territory  was  39  days,  from  April  7  at  Ellijay  to  May  16 
at  Blowing  Rock.  The  shortest  period  of  bloom  at  any 
station  was  10  days  at  Mount  Airy  and  the  longest,  27 
days,  at  Ellijay  and  Highlands. 

The  bloom  period  is,  of  course,  the  time  of  injury  to 
the  fruit  crop.  After  the  fruit  sets  and  the  leaves  come 
out  the  trees  become  less  susceptible  to  injury  as  each 
day  passes.  In  addition  to  the  injurious  effects  of  wind, 
which  will  be  noted  later,  it  will  be  seen  from  the  table 
that  two  frosts  or  freezes  occurred  over  the  whole  terri¬ 
tory  during  the  bloom  period  or  shortly  thereafter.  These 
were  April  22-28  and  May  11—12.  The  minimum  read¬ 
ings  for  the  April  22-28  storm  at  the  different  stations 
were  as  follows; 


Table  2. — Temperatures  at  different  slope  stations ,  freeze  of 
April  22-28,  1913. 


Location. 

No.  l,base 
station. 

No.  2,  on 
slope. 

No.  3,  on 
slope. 

No.  4,  on 
slope. 

No.  5;  top 
station. 

d 

d 

d 

d 

d 

4^ 

1 

4-3 

g 

.J 

a 

4-> 

1 

4-J 

a 

< 

* 

fr 

<• 

H 

< 

£ 

Feet. 

O 

Feet. 

0 

Feet. 

O 

Feet. 

O 

Feet. 

0 

Altapass . 

2,230 

35 

SE.,  250 

34 

SE.,  500 

33 

SE.,  750 

32 

1,000 

30 

Asheville . 

2,445 

33 

N.,  155 

32 

N.,3S0 

32 

S.,  155 

32 

2  S.,  380 

32 

Blantyre . 

2,090 

26 

NW.,  300 

32 

35 

NW.,  600 

36 

Blowing  Rock. . 

3, 130 

32 

SW.,  450 

32 

SE.,  450 

31 

SE.,  625 

32 

SE.,  800 

31 

Bryson  City. . . . 

1,800 

35 

N.,  385 

34 

1  S.,  385 

34 

570 

34 

Cane  River . 

2,650 

31 

N.,  210 

33 

NE.,  400 

30 

1,100 

?9 

Ellijay . 

2,  240 

32 

Ny  310 

34 

N7  620 

36 

N.,  1,240 

35 

1,760 

Globe . 

1,625 

3C 

E.,  300 

34 

1,000 

37 

Gorge . 

1,400 

29 

NE.,  290 

27 

E.,  615 

31 

W.,  840 

34 

1,040 

39 

Hendersonville. 

2,  200 

29 

E.,  450 

30 

E.,  600 

40 

E.,  750 

42 

Highlands . 

3, 350 

31 

SE.,  200 

30 

SE.,  325 

29 

SE.,  525 

28 

SE.,  725 

29 

Mount  Airy . 

1,3(0 

32 

W.,  160 

35 

E.,  160 

32 

360 

36 

Transon . 

2,970 

23 

W.,  150 

30 

W.,  300 

31 

450 

32 

Tryon . 

950 

30 

SE.,  3S0 

46 

SE.,  570 

47 

SE.,  1,000 

Waynesville. .. . 

2,900 

25 

N.,  150 

30 

N.,  320 

32 

Wilkesboro . 

1,240 

31 

N.,  150 

34 

N.,  350 

38 

W.,  430 

«l . 

>  Station  No.  2a.  »  Station  No.  3a. 


101 


THERMAL  BELTS  FROM  THE  HORTICULTURAL  VIEWPOINT. 


The  direction  of  the  slope  and  the  height  of  each  station 
above  the  base  stations  are  given  in  the  columns  before 
the  temperature  figures.  In  columns  3,  4,  and  5  if  no 
direction  of  slope  is  given  before  the  altitude  figure  it  is  a 
summit  station.  The  interpretation  of  these  data  I  will 
leave  to  the  meteorologist.  From  the  horticultural 
standpoint  it  will  be  noted  that  there  were  decidedly 
beneficial  theimal  conditions  on  the  slopes  of  the  orchard 
at  Blantyre  at  stations  3  and  4,  amounting  to  3°  and  4° 
o  P^°^ec^on.-  Station  No.  2  at  Cane  River  seems  to  have 
1  °t  protection  in  this  storm.  At  Ellijay  all  the  stations 
above  the  base  were  well  within  the  safety  range.  At 
Globe,  the  two  hill-side  stations  had  2°  and  5°  of  safety, 
respectively.  At  Gorge  the  two  upper  stations  had  "a 
decided  immunity,  as  also  had  the  two  upper  stations 
at  Hendersonville.  There  was  frost  at  Mount  Airy  at 
the  two  basal  stations  on  each  side  of  the  ridge,  while 
the  middle  and  top  stations  were  well  above  freezing. 
The  most  remarkable  thermal  conditions  are  shown  at 
Try on,  where  there  were  two  degrees  of  frost  at  the  basal 
station  in  the  valley  while  the  hillside  stations  Nos.  2,  3, 
and  4  had  14°,  15°,  and  13°,  respectively,  above  freezing. 
At  Wilkesboro  there  was  frost  only  at  the  bottom  station, 
with  all  the  hill  stations  standing  well  above  the  danger 
line.  A  summing  up  of  these  data  will  show  that  at  20 
hillside  stations  no  frost  occurred,  while  at  other  points 
above  or  below  in  these  same  orchards  there  were  freezing 
conditions  that  would  either  have  killed  or  injured  the 
blossoms  at  this  critical  time.  If  no  other  injury  had 
occurred,  the  fruit  at  these  20  stations  would  have  passed 
safely  to  a  good  harvest  later.  Where  the  second  frost 
did  not  occur,  as  at  Mount  Airy  and  Tryon,  the  con¬ 
clusions  above  were  shown  to  be  correct.  Heavy  crops 
of  fruit  were  gathered  at  both  of  these  points. 

Looking  further  over  the  data  of  the  above  tables,  it 
would  appear  that  at  the  high  altitudes  of  Altapass, 
Blowing  Rock,  Cane  River,  and  Highlands  the  fruit  at 
the  upper  stations  was  killed  by  “  high  top  freezes.” 

Some  of  the  observers  reported  a  frost  occurring  on 
May  11-12,  but  a  careful  perusal  of  the  instrument  trace 
sheet  shows  no  sign  of  it  in  the  orchard.  It  must  have 
been  seen  by  the  observers  in  low  places  and  reported 
accordingly.  However,  frost  did  occur  at  several  of  the 
higher  stations,  as  will  be  seen  from  the  following  table: 


Table  3. — Temperatures  at  different  stations  in  cold  spell  of 
May  11-12,  1913. 


Station. 

No.  l,base 
station. 

No.  2,  on 
slope. 

No.  3,  on 
slope. 

No.  4,  on 
slope. 

4-» 

< 

d 

a 

© 

H 

3 

d 

a 

© 

& 

d 

a 

© 

H 

< 

Blowing  Rock. . 
Bryson  City. . . . 

Cane  River . 

Gorge . 

Highlands . 

Transon . 

Waynesville... . 
Wilkesboro . 

Feet. 
3, 130 
1,800 
2,650 
1,400 
3, 350 
2,970 
2,900 
1, 240 

o 

30 

31 
30 
30 
43 
25 
29 
34 

Feet. 

SW.,450 

N.,385 

N.,190 

NE.,290 

SE.,200 

W.,150 

N.,150 

N.,150 

o 

31 
33 

32 
29 
46 
31 

33 
38 

Feet. 
E.,450 
1  S.,385 
NE.,400 
E.,615 
SE.,325 
W.,300 
N.,300 
N.,350 

o 

23 

36 

33 

31 

29 

31 

35 

41 

Feet. 
E.,625 
570 
1, 100 
W.,S40 
SE.,525 
450 

W.,430 

Top 

station. 


E. 

a 


© 

EH 


5 


31 
42 
33 
36 
39 

32 


Feet. 

800 


1,040 

SE.,725 


40 


d 

a 

© 

e 


31 


40 

40 


1  Station  No.  2a. 


From  the  table  above  it  will  be  seen  that  there  is 
a  very  cold  spot,  or  "frost  pocket,”  about  station  No. 
3  at  Blowing  Rock,  where  the  temperature  was  9° 
below  the  freezing  point,  while  no  other  station  in  this 
orchard  showed  over  2°.  The  station  at  this  point  is 
located  on  the  bank  of  an  artificial  lake,  with  a  dam 
and  timber  on  one  side  and  high  banks  on  all  other 
sides.  This  forms  a  bowl  into  which  the  cold  air  drains 
and  collects.  The  results  of  the  hard  frost  about  this 


station  showed  a  striking  contrast  with  conditions  else¬ 
where  in  the  orchard.  Fruit  was  completely  killed 
about  station  No.  3  and  to  an  approximate  height  of 
60  feet  above  it.  The  observer  stated  that  even  the 
leaves  were  frozen,  and  he  pointed  out  signs  of  this  to 
Mr.  Denson  and  myself  when  making  our  inspection  of 
the  station  on  September  19,  over  four  months  later. 

I  lie  results  of  this  injury  were  in  evidence  even  a 
year  later.  In  his  1914  report  the  observer  stated 

The  trees  near  station  No.  3  (for  a  height  of  approxi¬ 
mately  60  feet)  show  effect  of  the  damage  of  May  10-11, 
1913.  While  the  bloom  was  generally  heavy  elsewhere 
it  was  notably  light  in  this  portion  of  the  orchard.” 
Within  the  next  50  feet  above  there  were  scattered 
apples.  About  station  No.  2  in  the  China  orchard 
some  of  the  trees  were  full,  the  yield  increasing  upward 
through  the  orchard.  Near  the  base  station,  situated 
m  the  China  orchard  at  an  altitude  of  3,650  feet,  was 
a  plantation  of  grapes  that  at  the  time  of  our  visit 
(September  19)  were  just  ripening.  They  showed  a 
heavy  yield  of  fruit,  while  apple  trees  near  by  had 
little  or  no  crop.  This  was  doubtless  due  to  the  later 
blooming  period  of  grapes.  It  is  interesting  to  note 
that  the  same  varieties  of  grapes  were  ripe  at  Tryon 
at  an  altitude  of  1,275  feet  on  August  16,  showing  a 
difference  in  season  of  one  month  and  three  days. 

It  will  be  noted  that  in  all  of  the  other  orchards  showing 
frost  the  coldest  place  was  at  the  bottom  station,  except 
at  station  No.  2  at  Globe  and  station  No.  3  at  Highlands, 
nearly  all  the  hill  stations  showing  a  high  immunity 
from  injury.  Station  No.  3  at  Highlands  lies  at  the 
bottom  of  a  narrow  valley  surrounded  by  timber.  The 
cold  air  traps  in  this  natural  bowl  and  forms  a  constant 
frost  pocket.  This  is  abundantly  shown  by  succeeding 
records.  On  the  night  of  May  11  the  observer  at  Wilkes¬ 
boro  reports  a  heavy  frost  below  station  No.  1  and  above 
No.  4.  This  is  significant,  as  frost  will  not  occur  unless 
there  is  dew,  and  it  is  a  common  observation  of  thermal 
belts  that  they  are  dewless  and  frostless.  The  yields  of 
fruit  for  the  season  for  the  different  orchards,  as  shown 
in  Table  No.  1,  confirms  the  frost  data  as  recorded  by  the 
instruments  and  observers.  From  the  records  of  the 
instruments  and  also  from  the  reports  of  the  station  and 
observers  it  was  seen  early  in  the  season  that  the  spring 
of  1913  was  a  precarious  one  for  fruit.  Storm  followed 
storm  over  the  Blue  Ridge  after  a  period  of  nearly  three 
weeks  of  abnormally  warm  weather  in  March.  This 
long  warm  spell,  with  temperatures  ranging  in  the 
sixties,  started  growth  in  the  tissue  and  softened  the 
buds,  even  though  it  was  not  apparent  at  the  time. 
Then  followed  the  storm  of  March  27-28.  No  bloom 
had  yet  appeared.  The  earliest  record  of  bloom  at  any 
station  was  at  Ellijay  on  April  7.  The  other  stations 
followed  on  after  this,  with  records  of  final  bloom  up  to 
May  1  at  Blowing  Rock.  On  March  27  following  this 
extended  warm  spell  the  temperatures  at  most  of  the 
stations  dropped  from  the  sixties  to  freezing  and  to 
5°  to  16°  below  32°  F.  In  addition  to  these  low  tem¬ 
peratures  recorded  a  hard  cold  wind  swept  oyer  the 
orchards  from  24  to  48  hours.  This  peculiar  combination 
of  unfavorable  conditions  produced  a  result  new  to  me  in 
all  my  horticultural  experience — namely,  that  the  apple 
bloom  was  killed  in  bud.  Where  the  low  temperatures 
and  winds  were  most  severe,  the  trees  dropped  off  their 
fruit  buds  and  never  bloomed  at  all.  In  other  places 
the  bloom  was  sparce  and  feeble  and  the  fruit  dropped 
early.  As  a  contrast  to  this,  at  the  Mount  Airy  station, 
though  the  temperature  dropped  as  low  as  20°,  a  heavy 
crop  was  produced. 


102 


SUPPLEMENT  NO.  19. 


At  most  of  the  stations  the  blasting  effects  of  the  hard 
wind  was  more  injurious  than  the  low  temperatures, 
for  almost  invariably  it  was  the  upper  or  exposed  stations 
that  suffered  most.  On  this  subject  the  observer  at 
Bryson  City,  Capt.  A.  M.  Frye,  reports  as  follows:  “That 
part  of  the  basin  facing  south  and  having  unusually 
good  protection  from  high  wind  shows  an  average  yield, 
with  quite  a  number  of  trees  in  the  lower  part  full,  but 
the  opposite  slope  in  the  basin  facing  north  has  no  fruit.” 

The  observer  at  Ellijav,  Charles  G.  Mincy,  reports: 
“All  fruit  on  upper  slope  killed  in  bud  by  high,  cold, 
north  wind.”  Mr.  Julius  Gragg  at  the  Globe  station 
reports:  “There  is  practically  no  fruit  on  the  upper 
slopes  in  this  vicinity,  but  the  lower  slopes  and  bottoms 
in  some  places  show  good  results,  especially  where  there 
is  good  air  drainage  and  protection  from  wind.”  The 
late  M.  C.  Toms,  formerly  observer  at  the  Hendersonville 
station,  reports  upon  the  1913  crop  as  follows:  “Almost 
a  complete  failure,  only  a  few  trees  of  Mother  and  Virginia 
Beauty  (late  bloomers)  with  fruit.  This  orchard  is 
situated  above  a  plain  and  is  exposed  for  the  most  part 
to  the  full  force  of  the  wind  at  that  elevation.”  Mr. 
Denson  remarked  that  “It  is  an  interesting  comparison 
to  note  the  results  from  this  orchard  and  that  at  Mount 
Airy,  a  thousand  feet  lower,  with  the  protecting  wall  of 
the  main  Blue  Ridge,  which  orchard  bore  practically  a 
full  crop.  Mr.  Joseph  L.  Welch,  observer  at  Waynesville, 
remarks  that  “The  most  damage  was  done  on  high  and 
exposed  points  where  winds  had  a  fair  sweep.  Most 
yield  is  in  low  ground  and  where  trees  were  protected 
from  full  force  of  cold  winds.” 

The  season  of  1912  was  a  bumper  fruit  year  in  North 
Carolina.  One  grower  wittily  expressed  it  by  saying 
that  “Trees  that  had  been  dead  for  five  years  were 
heavily  loaded  that  year.”  A  late  spring  without  frosts 
following  a  good  “old-fashioned”  steady  winter  gave 
just  the  combination  necessary  to  assure  a  good  crop. 
The  apple  tree  is  normally  an  alternate  bearer,  because 
the  fruit  is  borne  on  twigs  that  takes  two  years  to  develop. 
So  a  year  of  full  crop  wnere  there  has  been  a  heavy  drain 
on  the  energies  of  the  tree  will  usually  be  followed  by  a 
weaker  bud  development  and  lighter  crop  the  following 
season.  From  this  it  would  appear  that  apple  orchards 
went  into  the  season  of  1913  with  more  or  less  of  a  handi¬ 
cap,  and  the  exceedingly  light  crop  harvested  in  the  high 
mountain  sections  is  undoubtedly  due  to  the  weakened 
bloom  being  subjected  to  extreme  vicissitudes  of  weather. 

LATE-BLOOMING  VARIETIES. 

A  point  of  decided  horticultural  interest  and  value 
brought  out  by  these  observations  is  the  fact  that 
varieties  of  apples  were  found  that  bloomed  from  10  days 
to  two  weeks  later  than  the  usual  standard  varieties. 
These  varieties,  given  in  order  of  their  lateness  of  bloom, 
are  Ingram,  Mother,  Virginia  Beauty,  Stark,  and  Gragg 
(a  local  variety).  In  this  decidedly  off  year  for  fruit 
the  orchard  in  which  the  Asheville  observation  station  is 
located  had  a  full  crop  of  apples  on  the  Ingram  variety, 
which  bloomed  two  weeks  later  than  other  varieties, 
and  on  Virginia  Beauty,  blooming  10  days  later,  one- 
fourth  of  a  crop,  while  other  varieties  in  the  orchard 
only  averaged  5  per  cent  of  a  crop.  There  were  no 
Ingram  or  Mother  apples  at  the  Blantyre  station,  but 
Virginia  Beauty  there  exceeded  all  varieties  in  yield 
owing  to  its  habit  of  late  blooming.  The  varieties  that 
gave  best  yield  at  Blowing  Rock  were  Mother,  Gragg, 
Stark,  Ingram,  Virginia  Beauty,  and  Jonathan,  nearly  all 


of  them  late  bloomers.  Mr.  T.  G.  Harbison,  observer 
at  the  Highlands  station,  reports  his  variety  yield  as 
follows:  “Ingram  (late bloomer), full  crop;  Northern  Spy, 
Black  Ben,  and  Gano,  above  average;  Ben  Davis  and 
Champion,  below  average;  Wealthy,  Delicious,  and 
Grimes  Colden,  scattering.” 

In  1914  the  observer  at  Blowing  Rock  reported  the 
varieties  Mother  and  Virginia  Beauty  as  being  in  bloom 
there  13  days  later  than  other  varieties. 

FRUIT  REPORT  FOR  1914. 

The  year  1914  was  known  as  “a  good  fruit  year” 
over  practically  the  whole  State.  There  were  no  freezes 
during  or  following  the  bloom  period,  and  only  2  out  of 
the  16  observing  stations  reported  any  frost.  These 
were  at  Altapass  on  April  7  and  at  Blantyre  on  April  8. 

The  first  bloom  reported  on  peaches  was  at  Tryon  on 
March  28,  and  the  latest  date  of  first  bloom  was  at  Blowing 
Rock  on  April  22,  25  days  later.  The  period  of  full 
bloom  over  all  tfie  stations  lasted  from  April  2  at  Tryon 
to  April  26  at  Blowing  Rock,  a  period  of  24  days.  The 
last  peach  bloom  reported  at  any  station  was  at  Blowing 
Rock  on  May  5.  It  will  be  noted  that  Tryon  and  Blowing 
Rock  represent  the  two  extremes  for  early  and  late  bloom 
and  that  there  is  a  general  difference  in  altitude  between 
these  stations  of  2,000  feet.  The  extreme  differences  in 
time  range  in  first  apple  bloom  are  found  between  the 
same  stations,  Tryon  and  Blowing  Rock,  the  first  being 
at  Tryon  on  April  15  and  the  last  at  Blowing  Rock  on 
May  3,  18  days  later.  The  range  of  apple  bloom  over 
all  the  stations  covered  a  period  of  36  days  from  April 
15  at  Tryon  to  May  21  at  Blowing  Rock.  No  frost  is 
reported  by  any  of  the  observers  as  occurring  within 
this  period.  The  apple  crop  of  1914,  thus  unaffected 
by  frost  or  cold,  turned  out  to  be  a  heavy  one,  the  only 
setbacks  being  from  blight  and  drought.  The  most 
extended  period  of  bloom  at  any  station  was  23  days  for 
peaches  at  Blantyre  and  22  days  for  apples  at  Highlands. 

On  investigation  of  the  injury  to  peach  bloom  reported 
at  Altapass  on  April  9,  the  instrument  record  shows  the 
following  minimum  temperatures  at  the  different  stations : 
Base,  27°;  No.  2,  25°;  No.  3,  25°;  No.  4,  24°;  summit,  22°. 

It  will  be  noticed  that  the  warmest  place  is  at  the  base 
and  the  coldest  place  at  the  summit  station.  No  apples 
were  in  bloom  at  this  time,  but  in  a  peach  orchard  located 
below  No.  3  station  on  the  slope  the  Elberta  peaches 
(earliest  bloomers)  were  just  coming  into  full  bloom. 
A  temperature  of  7°  below  freezing  would  naturally  be 
very  injurious  at  this  time.  The  observer  at  this  station 
reports  the  following  peculiar  phenomenon:  On  a 
20-acre  plot  just  below  station  No.  3  in  peaches  young 
trees,  mostly  Elberta,  one  half  Avas  killed,  while  the  other 
half  was  in  good  bearing ;  trees  of  the  same  age  and  under 
same  method  of  cultivation;  practically  no  difference 
in  elevation;  a  very  slight  rise  in  the  ground  between  the 
two  sections.”  In  this  case  there  was  a  very  evident 
thermal  belt  on  the  slope,  and  the  upper  edge  of  it  had 
been  about  halfway  up  through  this  peach  block,  as 
was  shown  by  a  failure  of  fruit  above  this  line  and  a 
good  crop  below  it.  During  the  same  cold  spell  frost 
was  reported  at  Blantyre,  but  almost  exactly  opposite 
conditions  prevailed  on  the  slope  stations  from  those 
reported  above  at  Altapass.  Both  the  slope  stations 
showed  lower  minima  than  either  the  base  or  summit 
stations,  and  peaches  at  these  points  suffered  a  logs  of 
one-third  of  the  crop. 


THERMAL  BELTS  FROM  THE  HORTICULTURAL  VIEWPOINT. 

_ _ Table  4. — Summary  of  horticultural  data  for  season  of  1914. 


103 


Location. 

Apples. 

Peaches. 

Cause  of  injury. 

Date  of 
injury. 

First 

bloom. 

Full 

bloom. 

Bloom 
all  shed. 

Dura¬ 

tion 

of 

bloom. 

Character 
of  bloom. 

First 

bloom. 

Full 

bloom. 

Bloom 
all  shed. 

Dura¬ 

tion 

of 

bloom. 

Character 
of  bloom. 

Days. 

Days. 

Altapass . ,. 

Apr.  25 

May  1 

May  8 

13 

Average. 

Apr.  5 

Apr.  17 

Apr.  26 

21 

Average. 

Frost . 

Apr.  7 

Asheville . 

Apr.  19 

Apr.  29 

May  3 

14 

. .  .do _ 

Apr.  9 

Apr.  13 

Apr.  21 

12 

. .  .do . 

Drought . 

Blantyre . 

Apr.  20 

Apr.  26 

May  6 

16 

Light . . . 

Apr.  1 

Apr.  7 

Apr.  24 

23 

(l) 

Apr.  8 

Blowing  Rock.... 

May  3 

May  8 

May  21 

18 

Heavy. . 

Apr.  22 

Apr.  26 

May  5 

13 

Bryson  City . 

Apr.  16 

Apr.  21 

Apr.  26 

11 

Cane  River . 

Apr.  23 

Apr.  30 

May  8 

15 

. .  -do _ 

Ellijay . 

Apr.  17 

Apr.  25 

Mav  5 

18 

. . .do - 

Apr.  7 

Globe . 

Apr.  21 

Apr.  26 

May  3 

10 

...do . 

Apr.  7 

Apr.  17 

Apr.  24 

17 

Gorge . 

Apr.  20 

...do _ 

. .  .do — 

13 

. .  .do _ 

. .  -do . 

Apr.  16 

. .  .do . 

17 

None . 

Hendersonville. . . 

Apr.  22 

Apr.  27 

May  5 

13 

Average. 

Apr.  3 

Apr.  13 

Apr.  20 

17 

Highlands . 

Apr.  23 

Apr.  29 

May  15 

22 

. . .do . 

(2) 

Mount  Airy . 

Apr.  20 

Apr.  26 

May  5 

15 

Heavv . . 

Apr.  1 

Apr.  12 

Apr.  21 

20 

Heavy. . 

Transon . 

Apr.  25 

May  4 

May  14 

19 

. .  .do . 

Apr.  20 

Apr.  24 

8 

Trvon . 

Apr.  15 

Apr.  22 

Apr.  29 

14 

Average. 

Mar.  28 

Apr.  2 

15 

Waynes  vilie . 

Apr.  18 

Apr.  24 

Apr.  30 

12 

Heavv. . 

Mar.  30 

Apr.  5 

Apr.  15 

16 

Wilkesboro . 

Apr.  16 

Apr.  23 

i 

May  1 

15 

Average. 

Apr.  3 

Apr.  12 

Apr.  22 

19 

Loss  by 
May 
drop. 


Light . . . 
Heavy . . 
Light... 
Average. 
Light . . . 

...do _ 

...do . 

Average. 

...do . 

Heavy. . 

...do . 

Average. 

Light... 

Average. 

Light... 

Average. 


Yield 
of  ap¬ 
ples 


P.ct. 

80 

25 

100 

50 

100 

85 

75 

95 

95 

50 

50 

80 

95 

80 

70 

80 


Yield  !  A1H 
of  1  ^Im¬ 
peaches  i  tuc*e- 


66 


95 


100 


70 

80 

75 


P.ct.  '  Feet 

50  I2-230- 
0U  \  3,230 

(2,445- 

. 2.825 

(2,090- 
\  2,690 
1(3,130- 
\  3,930 
(1,800- 
\  2,370 
2,650- 
3,750 
2,240- 
4,000 
(1,625- 
V  2,625 
(1,400- 
\  2,440 
(2,200- 
\  2,950 
(3,350- 
l  4,075 
(1,340- 
\  1,700 
'2,970- 
3,420 
950- 
2, 0601 
(2,900-' 

\  3,200 
/l, 240-1 
\  1,670;/ 


Range 
of  alti¬ 
tude. 


Feet. 

1,000 

380 

}•  600 
}■  800 
570 
1,100 
1,760 
1,000 
1,040 
750 
725 
360 
450 
1,110 
320 
430 


1  Apples,  none;  peaches,  frost. 

FRUIT  CROP  REPORT  FOR  1915. 


The  year  1915  in  North  Carolina  was  a  favorable  one 
for  fruit  production  as  far  as  exemption  from  cold  and 
frost  is  concerned,  for  not  a  single  unfavorable  report 
came  from  any  of  the  observing  stations  regarding  in¬ 
jurious  temperatures.  The  peach  crop  was  much  above 
the  average  in  all  sections  of  the  State,  and  as  the  behavior 
of  this  tender  fruit  gives  a  good  index  of  frost  conditions 
it  seems  safe  to  say  that  there  was  little  or  no  injury  to  any 
class  of  fruits  from  unfavorable  temperatures.  This, 
while  very  gratifying  to  the  fruit  growers  in  a  practical 
way,  was  unfavorable  from  the  standpoint  of  recording 
data  on  thermal  belts,  and  little  evidence  was  forth¬ 
coming  from  the  year’s  records. 

The  apple  crop  in  the  State,  even  with  the  uniformly 
favorable  thermal  conditions,  did  not  amount  to  over  40 
per  cent  of  a  full  crop,  but  the  injury  was  due  to  drought 


2  Peaches  never  bloomed;  killed  in  bud  Mar.  2,  when  temperature  dropped  to  5°  F. 

and  especially  to  twig  blight,  which  was  very  destructive 
this  year  to  the  apple  and  pear  crop  throughout  the 
whole  country. 

A  striking  and  rather  remarkable  injury  occurred  in 
the  orchard  under  observation  at  Blowing  Rock.  The 
observer,  Mr.  E.  G.  Underdown,  describes  it  as  follows: 
“Crop  almost  a  complete  failure  in  home  and  China 
orchards.  Buds  knocked  off  by  extraordinarily  heavy 
hail  on  April  23  just  as  they  were  beginning  to  swell. 
The  ground  was  covered  with  buds,  and  the  hail  bruised 
the  trees  to  such  an  extent  as  to  effect  the  prospects  for 
next  year.  Hail  was  three  to  four  inches  in  depth  and 
remained  on  the  ground  in  places  for  a  week.  A  light 
bloom  followed  in  about  10  days,  but  most  of  it  shed 
without  forming  fruit,  and  the  fruit  that  formed  dropped 
shortly  afterwards.  Hail  did  not  extend  to  the  Green 
Park  orchard,  which  bore  a  fair  crop,  but  there  was 
considerable  damage  from  blight.” 


Table  5. — Summary  of  horticultural  data  for  season  of  1915. 


Location. 


Altapass . 

Asheville . 

Blantyre . 

Blowing  Rock.. . 

Bryson  City . 

Cane  River . 

Ellijay . . 

Globe . 

Gorge . 

Hendersonville. . 

Highlands  Nos. 
1-2. 

Highlands  Nos. 
3-5. 

Mount  Airy . 

Transon . 

Tryon . 

Wilkesboro . 


Apples. 


First 

bloom. 


Full 

bloom. 


Apr.  25 
Apr.  22 
Apr.  21 
Apr.  29 
Apr.  19 
Apr.  23 
Apr.  20 
...do.. . 
Apr.  19 

Apr.  20 
Apr.  19 

Apr.  26 

Apr.  10 
Apr.  24 
Apr.  10 
Apr.  14 


Apr.  30 
Apr.  28 
Apr.  26 
May  8 
Apr.  26 
May  2 
Apr.  24 
Apr.  25 
Apr.  28 

Apr.  27 
...do... 
Apr.  13 

Apr.  14 
May  1 
Apr.  16 
Apr.  20 


Bloom 
all  shed. 


May  5 
May  3 
May  9 
May  12 
May  2 
May  9 
May  4 
May  1 
May  8 

May  6 
.. .do. . . 

May  8 

May  22 
May  7 
Apr.  23 
Apr.  28 


Dura 

tion 

of 

bloom. 

Days. 

10 

11 

18 

13 

13 
16 

14 
11 
19 

16 

17 

12 

12 

13 

13 

14 


(Light  to  1 A  18 
\  average.  /  1 

Apr.  8 

Apr.  14 


Character 
of  bloom. 


Average . 

. .  .do _ 

Heavy . . 


average. 

Average. 

Heavy. . 
Light . . . 

.  .do _ 

.  .do _ 

Average. 

..do _ 

..do _ 

...do _ 

Light . . . 
Average. 
Heavy.. 


Peaches. 


First 

bloom. 


Apr.  14 
Apr.  10 
..do.. . . 


Apr.  9 
Apr.  5 
Apr.  10 

Apr.  9 

Apr.  6 
Apr.  20 
Mar.  27 


Full 

bloom. 


Apr.  20 
Apr.  18 
Apr.  15 
Apr.  24 
Apr.  15 
Apr.  20 


Apr.  16 
Apr.  12 
Apr.  19 

Apr.  14 

Apr.  13 
Apr.  25 
Apr.  5 


Bloom 
all  shed. 


Apr.  25 

. .  .do _ 

May  3 
Apr.  30 
Apr.  24 
May  1 


Apr.  26 
Apr.  27 
Apr.  24 

Apr.  20 

...do . 

Apr.  30 
Apr.  9 


Dura¬ 

tion 

of 

bloom. 


Days. 

11 

15 
23 
12 

16 
17 


Character 
of  bloom. 


Average . 


Heavy . . 


/Blight  and  \ 
\  drought.  /• 


Average. 

..  .do _ 

Light . . . 
Average. 

...do _ 

. . .do... . 
Light . . . 
Average. 
Heavy.. 


Cause  of  injury. 


Blight . . 

(l) 

Blight,  drought 
Heavy  hail.... 


drought. 
Cold  wind 


Blight . 

_ do . 

Blight,  wind. 


Cold  wind. 


Blight . 

Blight,  wind. 


Date  of 
injury. 


Apr.23 


Loss  by 
May 
drop. 

Yield 
of  ap¬ 
ples. 

P.  ct. 

Average . 

33 

Heavy. . 

50 

15 

..  .do _ 

5 

...do _ 

50 

Light . . . 

20 

Heavy . . 

25 

Light . . . 

20 

25 

Heavy.. 

20 

Light... 

65 

50 

5 

Light . . . 

85 

/Very 
\  light. 

}  90 

Yield 

of 

peaches 


P.ct. 

80 


90 


Alti¬ 

tude. 


80 

75 

75 

35 


100 

5 

90 

95 


Feet. 
2, 230- 
3,230 
’2,  445- 
2,825 
’2,090- 
2,690 
’3, 130- 
3,930 
1,800- 
2,  370 
2,650- 
3,760 
2,240- 
4,000 
1,625- 
2,625 
1,400- 
2,410 
'2,200- 
2,950 

13, 350- 
\4,07- 

1,340- 
1,700 
f2,970- 
13,420 
f  950- 
12,060 
’l,  240- 
[1.670 


Range 
of  alti¬ 
tude 


Feet 

1,000 

380 

600 

800 

570 

1,100 

1,760 

1,000 

1,040 

750 

725 

360 
450 
1, 100 
430 


Apples,  blighted;  peaches,  uninjured. 


104 


SUPPLEMENT  NO.  19. 


THE  DANGER  PERIOD  OF  1916. 

The  spring  season  of  1916,  as  shown  by  the  starting 
of  plant  growth  at  the  different  stations,  was  from  one 
to  two  weeks  earlier  than  in  1915.  This,  of  course,  gave 
that  much  more  time  for  unfavorable  temperatures  than 
would  occur  in  a  normal  or  late  season,  and  for  that 
reason  the  early  spring  of  1916  was  marked  by  sharp 
declines  in  temperature  after  growth  started,  with  a 
resultant  lessening  of  the  fruit  crop.  In  February  and 
March  previous  to  the  starting  of  vegetation  such  low 
temperatures  were  recorded  that  most  of  the  peaches 
were  killed  in  bud,  and  the  bloom  that  did  come  out  was 
scanty  and  irregular.  The  earliest  bloom  of  peaches 
recorded  was  at  Tryon,  on  March  13,  and  the  latest  bloom 
to  start  was  at  Globe,  March  28,  15  days  later.  The 
earliest  date  of  peach  bloom  being  shed  was  at  Tryon, 
on  April  3,  and  tne  latest  at  Bryson  City,  April  19.  The 
total  length  of  this  most  critical  period  to  the  crop  was 
37  days  over  the  whole  section  and  32  days  at  Bryson 
City,  which  was  the  longest  period  at  any  one  point. 
After  the  bloom  is  shed  the  fruit  is  more  or  less  protected 
for  some  days  by  the  “  shuck,”  which  is  the  dried  up 
calyx  tube.  Leaves  push  out  rapidly  at  this  time  and 
by  increasing  growth  give  greater  protection  to  the  fruit 
as  each  day  passes.  At  points  where  the  peaches  were 
not  entirely  killed  in  February  they  were  injured  by 
exceedingly  low  temperatures  of  the  cold  wave  of  March 
16.  The  minimum  temperatures  recorded  at  the  differ¬ 
ent  stations  during  this  storm  are  shown  in  the  following 
table : 

Table  6. 


No.  1,  base 
station. 

No.  2,  on 
slope. 

No.  3,  on 
slope. 

No.  4,  on 
slope. 

No.  5,  sum¬ 
mit. 

Location. 

d 

d 

d 

d 

d 

a 

a 

a 

• 

a 

* 

a 

3 

H 

< 

H 

< 

Eh 

< 

h 

3 

Eh 

Feet. 

Mu. 

Feet. 

Mn. 

Feet. 

Mn. 

Feet. 

Mn. 

Feet. 

Mn. 

Altapass . 

2,  230 

13 

SE.,  250 

11 

SE.,  500 

10 

SE.,  750 

8 

S.,  1,000 

6 

Asheville . 

2, 445 

11 

N.,  155 

8 

N.,  380 

11 

1  S.,  155 

8 

3  S.,  3S0 

10 

2,090 

14 

NW.,300 

13 

NW.,450 

12 

NW  ,  600 

12 

Blowing  Rock . . 

3j  130 

7 

SW,,  450 

4 

SE.,  450 

5 

SE.,  625 

4 

E.,  800 

2 

Brvson  City. ... 

1,800 

11 

N.,  385 

11 

1  S.,  385 

10 

570 

10 

2, 650 

8 

N.,  190 

9 

NE',  400 

8 

1, 100 

2 

Ellijay . 

2, 240 

10 

N.,  310 

12 

N.;  620 

9 

N.,  1, 240 

6 

1,760 

4 

Globe . 

1,625 

17 

E.,  300 

15 

1,000 

9 

Gorge . 

1,400 

17 

NE.,  290 

16 

E.,  615 

14 

Wj,  840 

12 

1,040 

12 

Hendersonville. 

2,200 

10 

E.,  450 

10 

E.,  600 

5 

E.,  750 

8 

Highlands . 

3, 360 

9 

SE.,  200 

7 

SE.,  325 

6 

SE.,  525 

3 

SE.,  725 

3 

Mt.  Airy . 

1,340 

16 

W.,  160 

14 

E.,160 

15 

360 

14 

Transon . 

2, 970 

7 

W.,  150 

6 

W.,  300 

5 

450 

4 

Tryon . 

950 

19 

SE.,  380 

18 

SE.',  500 

14 

SE.,  1,000 

13 

Wi'lkesboro . 

1,240 

16 

N.,  150 

15 

N.,  350 

17 

W.,  430 

15 

1  Station  No.  2a.  2  Station  No.  3a. 


After  a  glance  at  these  minimum  temperatures  re¬ 
corded  at  the  different  points  the  wonder  is  that  any 
fruit  survived  at  all,  especially  since  some  of  the  bloom 
had  burst  or  was  swelling  preparatory  to  doing  so  and 
was  therefore  in  a  tender  condition.  At  some  of  the 


stations  even  the  maximum  temperatures  for  the  24- 
hour  period  were  below  freezing. 

Fruit  buds  and  bloom  will  often  stand  a  drop  in  tem¬ 
perature  to  below  freezing  if  the  minimum  is  not  long 
endured,  but  when  the  low  temperature  is  maintained 
for  several  hours  little  or  no  fruit  will  survive.  At  the 
stations  of  high  altitude  where  the  very  low  tempera¬ 
tures  were  recorded  the  peach  crop  was  a  total  loss. 
This  happens  so  often  in  these  altitudes  that  no  attempt 
is  made  to  raise  peaches  commercially  above  an  altitude 
of  2,000  feet.  Above  this  general  altitude — that  is,  in 
the  Blue  Ridge  plateau — not  only  the  bloom  buds  but 
even  the  trees  are  sometimes  killed  outright  by  low 
temperatures.  In  all  this  region  peaches  are  only 
grown  in  gardens  and  protected  places  for  domestic  use. 
An  idea  of  the  low  temperatures  to  which  fruit  is  some¬ 
times  subjected  in  these  regions  can  readily  be  seen  by  a 
comparison  of  the  minimum  temperatures  recorded  in 
the  table  above  at  the  high  stations — Altapass,  Blowing 
Rock,  Ellijay,  Highlands,  and  Transon.  It  will  be 
noted  further  that  at  the  before-mentioned  stations  the 
lowest  temperature  recorded  was  in  every  case  at  the 
summit  station.  This  is  an  example  of  what  is  com¬ 
monly  known  in  these  sections  as  “high-top  freezes." 

Some  of  the  fruit  growers  in  these  higher  sections 
of  the  mountains  gave  experiences  they  had  had  with 
“high-top  freezes.”  While  we  were  locating  the  observ¬ 
ing  station  in  Captain  Frye’s  orchard  at  Bryson  City,  he 
pointed  to  a  flat-topped  mountain  a  thousand  or  more 
feet  higher  than  his  present  location  and  said  “I  had  an 
orchard  once  on  top  of  that  mountain,  but  it  was  killed 
out  by  high-top  freezes.” 

Mr.  J.  D.  Auld,  manager  of  the  Farm  Life  School  at 
Valle  Crusis,  N.  C.,  reports  on  May  15,  1916,  on  their 
orchard  which  is  located  in  a  valley  the  floor  of  which 
has  an  altitude  of  approximately  3,000  feet:  “Our 
Black  Ben  trees,  which  are  about  12  years  old,  are 
cracking  around  the  trunk  and  the  bark  is  breaking  off; 
will  you  please  advise  us  how  to  care  for  these  trees  and 
save  them?”  These  trees  were  evidently  killed  by  the 
very  low  temperature  of  the  cold  wave  of  March  16, 
reported  in  the  table  above. 

In  1911,  when  Prof.  Cox,  Mr.  Denson,  and  the  writer 
were  seeking  orchards  for  comparison  at  high  altitudes, 
we  visited  one  at  Elk  Park,  N.  C.,  where  the  owner, 
Mr.  McCowan,  pointed  out  a  section  where  he  said 
apple  trees  had  been  killed  year  after  year  by  high-top 
freezes.  In  speaking  of  the  cold  injury  to  trees  at 
these  high  altitudes,  I  would  not  care  to  leave  the  im¬ 
pression  that  there  are  a  great  many  locations  in  the 
mountains  where  it  is  impossible  to  raise  fruit,  but  at 
the  same  time  it  must  be  recognized  that  each  class  of 
fruits  has  its  altitude  limitations.  From  my  extended 
experience  with  apple  growing  in  the  humid  regions  1 
would  place  the  altitude  limit  for  commercial  apple 
growing  at  about  3,000  feet. 


THERMAL  BELTS  FROM  THE  HORTICULTURAL  VIEWPOINT. 


Table  7. — Summary  of  horticultural  data  for  season  of  1916. 


— 

- - -  ^  J 

Location. 

Apples. 

Peaches. 

Cause  of  injury. 

Date. 

Character 
of  bloom. 

Per  cent 
of  loss 
by  May 
drop. 

Yield. 

Altitude. 

Range 

in 

alti¬ 

tude. 

First 

bloom. 

Full 

bloom. 

Bloom 
all  shed. 

Dura¬ 
tion  of 
bloom. 

First 

bloom. 

Full 

bloom. 

Bloom 
all  shed. 

Dura¬ 
tion  of 
bloom . 

Altapass . 

Asheville . 

Blantyre . 

Blowing  Rock . 

Apr.  18 

Apr.  12 

Apr.  15 

Apr.  23 

...  do . 

...do . 

May  5 

May  7 

May  6 

Days. 

17 

25 

21 

Mar.  25 

Mar.  27 

Mar.  23 

Mar.  31 

Mar.  30 

Mar.  28 

Apr.  5 

. .  .do . 

Apr.  6 

Days. 

11 

9 

14 

Winter  killing. 

. 

Winter  cold. .. 

/Feb.  14, 
\Mar.  16 
/Feb.  14 
\Mar.  16 
/Feb.  3 
IFeb.  14 

}Light... 
j-Heavy . . 
jAverage. 

Average. 

Light . . . 

30 

Per  cent. 
Apples,  75 1 

55 

50 

Feet. 

2, 230-3, 230 

2,445-2,825 

2, 090-2, 690 

3, 130-3, 930 
1,800-2, 370 

2,650-3,750 

2.240- 4,000 
1,625-2,625 
1,400-2,440 

2,200-2,950 

3,350-4,075 

}l,  340-1, 700 
>2, 970-3, 420 

}  950-2,060 

1.240- 1,670 

Feet. 

1,000 

380 

600 

800 

670 

1, 100 

1,760 

1,000 

1,040 

750 

725 

360 

450 

1,000 

430 

Cane  River . 

Ellijay . 

Apr.  15 

Apr.  24 

May  18 

33 

Apr.  19 

Winter  killing. 

/Feb.  14 
\Mar.  15 

Average, 
j-.do . 

Light . . . 
Heavy. . 

100 

65 

Globe . 

Gorge . 

Hendersonville. . . . 

Highlands . 

Mount  Airy . 

Transon . 

Tryon . 

Wilkesboro . 

Apr.  2 

Apr.  17 

1  Apr.  15i 
\Apr.  22 8 
Apr.  13 

Apr.  20 
Apr.  5 

Apr.  4 

...do . 

Apr.  23 

Apr.  25 
Apr.  30 

Apr.  21 

May  7 
Apr.  13 

Apr.  17 

Apr.  30 
May  6 

May  7 

May  9 
May  14 

May  2 

May  18 
Apr.  25 

Apr.  28 

34 

20 

24 

22 

19 

28 

20 

24 

Mar.  28 
Mar.  14 

Mar.  24 

} . 

Mar.  24 

Mar.  26 

Mar.  13 

Mar.  14 

Apr.  2 
Apr.  1 

Mar.  30 

Apr.  5 

Mar.  31 

Mar.  25 

Mar.  28 

Apr.  16 
Apr.  8 

Apr.  6 

Apr.  16 

Apr.  4 
Apr.  3 

Apr.  8 

19 

25 

13 

23 

9 

21 

24 

Freeze . 

Frost . 

Winter  killing. 

Drought . 

Winter  killing. 

Frost . 

Winter  killing. 

Freeze . 

Mar.  16 

...do . 

(Feb.  14, 

■  Mar.  16, 
Mar.  28 

/Feb.  3, 
\Feb.  14 
(Apr.  28, 
\Apr.  30 
Feb.  14 

Mar.  16 

Average. 

jHeavy.. 

Average. 

}Light... 

} . 

Average. 

Heavy. . 

. .  .do . 

Average. 

20 

Light . . . 

75 

80 

50 

50 

/Apples,  80; 
l  peaches,  30. 
/Apples,  50; 

1  peaches,  50. 
/Apples,  85; 
\peaches,  60. 

25 

1  Peaches  mostly  killed  in  bud.  »  Stations  Nos.  1-2.  »  Stations  Nos.  3-5. 


FROST  POCKETS. 

A  type  of  local  injury  to  fruit  in  contrast  to  that  called 
"high-top  freezes”  is  found  in  certain  locations,  known  as 
"frost  pockets.”  These  frost  pockets  are  basin-like  de¬ 
pressions  of  greater  of  less  extent  formed  by  the  natural 
lie  of  theland  or  by  surrounding  hills  or  mountains.  Often 
the  pocket  or  hollow  is  accentuated  by  tall  timber,  which 
interferes  with  wind  and  natural  movements  of  the  air. 

During  the  period  of  these  investigations  several  of 
these  frost  pockets  were  discovered,  not  by  the  observers 
but  by  the  recording  instruments.  It  was  noted  that  at 
some  certain  points  the  instruments  habitually  recorded 
lower  temperatures  than  would  seem  to  be  warranted  by 
comparison  with  the  other  instruments  in  the  same  or¬ 
chard.  A  careful  check  on  the  clocks  and  recording  pens 
of  the  instruments  by  comparison  with  mercurial  thermom¬ 
eters  showed  no  mechanical  or  instrument  variations,  so 
the  persistently  lower  temperatures  must  be  due  to  local 
topographic  conditions.  A  description  of  these  persist¬ 
ently  low  temperature  points  will  bring  out  the  charac¬ 
teristics  of  these  "frost  pockets.” 

At  station  No.  3,  or  the  lake  station  at  Blowing  Rock, 
habitually  low  temperatures  were  recorded.  At  this 
point  the  instrument  is  located  a  few  feet  above  the  level 
of  an  artificial  lake  that  is  surrounded  by  high,  rather 
steep,  sloping  banks  on  three  sides  and  by  a  dam  and 
high  timber  on  the  fourth  side.  In  standing  at  the  instru¬ 
ment  shelter  the  observer  finds  himself  in  a  deep  basin,  of 
which  the  surface  of  the  lake  is  the  floor,  and  with  steep 
sides  sloping  rapidly  upward  in  every  direction.  When 
there  is  a  falling  temperature  and  no  disturbing  wind,  the 
air  as  it  cools  settles  naturally  into  this  depression,  and 
the  coldest  place  is  found  at  the  bottom  of  this  basin. 
Frost  after  frost  was  seen  in  spring  in  this  pocket  when 
none  was  in  evidence  in  other  parts  of  the  orchard.  On 
June  11,  1913,  the  temperature  at  this  station  dropped  to 
33°,  and  frost  occurred  in  this  pocket  though  in  no  other 
part  of  the  orchard  was  the  temperature  lower  than  38°. 
Attention  is  here  called  to  the  freezing  of  the  fruit  and 
leaves  on  the  apple  trees  in  this  pocket  on  May  10-11, 
1913,  as  recorded  for  the  data  of  that  year  on  page  — . 
On  December  15,  1914,  a  temperature  of  -5°  was  re¬ 
corded  by  the  instrument  in  this  cold  basin. 


Another  "frost  pocket,”  discovered  by  the  recording 
instrument  from  low  minimums,  was  at  station  No.  3  at 
Highlands.  The  instrument  here  is  located  in  a  little 
open  field  at  the  base  of  the  Waldheim  orchard.  The 
orchard  rises  above  it  on  a  southeast  slope  to  an  altitude 
of  500  feet.  This  little  field  at  the  base  of  this  high  slope 
is  completely  surrounded  by  high  timber  on  all  sides. 
The  station  at  this  point  is  characterized  by  persistently 
low  temperatures  and  frost.  In  his  1915  report  the 
observer  at  Highlands,  Mr.  T.  G.  Harbison,  says:  "There 
was  nearly  a  full  crop  of  apples  in  the  lower  orchard  and 
a  fair  crop  in  the  Waldheim  orchard  except  in  the  lower 
part  near  stationNo.3”.  This  was  in  one  of  the  seasons 
most  exempt  from  frost  that  we  have  had  in  years.  On 
December  15,  1914,  the  temperature  in  this  frost  pocket 
dropped  as  low  as  —7°.  On  June  12  and  14,  1913,  the 
instrument  went  as  low  as  32°,  and  the  same  low  point 
was  reached  on  June  10,  1916.  Another  instrument- 
discovered  frost  pocket  is  the  base  station  at  Tryon.  This 
station  is  located  near  the  Pacolet  River  in  a  rather  nar¬ 
row  valley  surrounded  by  low  hills  with  high  mountains 
beyond.  Low  temperatures  and  frosts  were  frequent  at 
this  point.  In  the  year  1914,  when  conditions  tor  fruit 
were  the  most  favorable  that  we  have  had  in  years,  the 
fruit  in  this  frost  pocket  at  Tryon  was  killed,  while  on  the 
slopes  above  it  there  was  a  bumper  crop.  The  observer, 
Mr.  W.  T.  Lindsey,  of  Tryon,  reports:  "There  were  no 
apples  in  orchard  below  near  station  No.  1;  apparently 
killed  by  frost.”  The  following  year  (1915)  this  frost 
pocket  lived  up  to  its  former  reputation,  and  Mr.  Lindsey 
makes  almost  asimilar  report  to  1914,  viz,  "Fine  crop  of 
grapes,  peaches,  apples,  and  figs  on  main  slope.  Very 
few  apples  on  orchard  at  station  No.  1;  apparently  killed 
by  frost.” 

The  early  fruit  growers  believed  that  the  valleys  sur¬ 
rounded  by  timber  to  protect  from  winds  were  the 
safest  places  in  which  to  plant  fruit  trees,  but  later  ex¬ 
perience  with  such  places  has  confirmed  the  results  of 
our  observations  that  such  places  are  usually  frost 
pockets  and  should  be  avoided.  The  abandoned  orchards 
found  in  many  such  locations  is  mute  testimony  to  their 
frostiness  and  resulting  unproductiveness.  The  interest 
in  these  thermal  belt  observations  in  the  mountains 
naturally  made  me  keenly  observant  of  frost  data  when- 


106 


SUPPLEMENT  NO.  19. 


ever  found.  I  have  thus  for  years  in  my  work  as  State 
horticulturist  kept  careful  note  of  frost  data.  A  few 
incidents  will  serve  to  confirm  the  data  recorded  above. 
At  our  experimental  substation  in  the  Coastal  Plain,  we 
had  a  sharp  frost  on  a  quiet  night  when  peaches  were  in 
full  bloom.  On  examining  and  counting  several  hundred 
of  the  injured  blooms  only  16  per  cent  of  living  pistils 
were  found  in  a  zone  2  feet  from  the  ground,  33  per  cent 
in  a  zone  from  2  to  4  feet  from  the  ground,  and  60  per 
cent  of  living  blooms  in  the  zone  from  4  feet  to  the  top 
of  the  trees.  Later  at  harvest  time  practically  all  the 
crop  was  gathered  from  the  upper  and  very  little  from 
the  lower  branches  of  the  trees.  Another  season  at  this 
experimental  substation  we  had  a  very  late  and  hard 
frost  that  came  when  the  pecans  were  in  bloom.  A 
very  conspicuous  frost  line  could  be  seen  on  the  trees 
about  10  feet  from  the  ground.  Below  this  line  the 
catkins  and  half-grown  leaves  were  destroyed  as  if  by 
fire,  but  above  this  line  the  bloom  and  foliage  were  un¬ 
injured.  Later  the  only  nuts  that  were  gathered  were 
from  the  tops  of  the  trees  above  10  feet.  The  same 
phenomenon  has  been  observed  in  the  dewberry  section, 
where  a  frost  line  showed  two-thirds  of  the  way  up  on  the 
staked  vines,  which  later  fruited  only  at  the  tops  of  the 
six-foot  stakes. 

Frost  lines  are  often  observed  in  spring  on  the  natural 
vegetation  in  the  woods.  In  the  Sandhill  section  of 
North  Carolina,  where  the  irregular  contour  of  the  land 
gives  a  great  many  dips  and  depressions,  frost  lines  are 
often  seen  in  spring  along  the  bottoms  and  "branches” 
in  frost-blackened  foliage  on  the  "black  jack”  oaks. 
These  phenomena  have  many  times  been  pointed  out  to 
me  by  the  peach  growers  in  this  section.  Such  phe¬ 
nomena  are  often  noted  by  fruit  growers  in  the  moun¬ 
tains.  Once  at  Blantyre,  before  we  began  thermal  belt 
observations,  Mr.  Collett,  our  superintendent,  called  my 
attention  to  a  frost  band  along  the  side  of  Fodderstack 
Mountain.  A  distinct  line  of  frost-bitten  vegetation 
could  be  seen  along  the  base  of  the  mountain  while 
higher  up  the  foliage  was  fresh  and  green. 

In  the  summer  and  fall  of  the  year  fog  lines  are  often 
seen  in  the  valleys  of  the  mountains  as  are  snow  lines 
in  winter.  The  temperature  in  the  valley  will  be  lowered 
sufficiently  to  condense  the  moisture  in  the  air  up  to  a 
certain  height,  which  may  be  seen  from  above.  The  fog 
will  follow  this  temperature  line  faithfully  into  every 
cove  or  depression  of  the  hills  and  will  appear  on  its 
upper  surface  as  level  as  a  floor.  In  1911,  when  Pro¬ 
fessor  Cox,  Mr.  Denson,  and  the  writer  were  making  our 
preliminary  survey  for  locating  the  thermal  observing 
stations  we  drove  on  July  4  from  Waynesville  to  the  top 

of - —  Mountain  and  stayed  over  night  at  the 

"Eagles  Nest”  hotel.  We  had  a  sunrise  call  for  the 
morning  and  were  well  repaid  by  rising  at  this  early  hour 
to  get  the  magnificent  view.  It  looked  more  like  a  sea 
or  lake  than  an  inland  mountain  valley,  for  fog  had 
stratified  until  it  looked  like  a  great  body  of  water  below, 
with  islands  showing  where  the  higher  hills  of  the  valley 
rose  above  the  level  upper  surfaces  of  the  fog. 

CONCLUSIONS. 

A  thermal  belt  is  not  a  fixed  and  definite  zone  whose 
boundaries  can  at  all  times  be  precisely  located.  Under 
some  combinations  of  weather  conditions  it  may  be  at 
the  base  of  a  slope  and  under  another  set  of  conditions 
at  the  top.  A  storm  or  strong  wind  may  so  mix  up  the 
air  that  it  may  be  nonexistent  or  temporarily  lost,  but 
when  normal  weather,  as  we  understand  it,  is  again 


restored  it  is  back  at  home  again  on  its  native  hillside 
giving  favorable  temperatures  along  the  slope.  We  can 
not  commonly  see  it  except  to  note  its  presence  in  frost, 
fog,  or  snow  lines,  but  it  is  there,  for  the  average  tempera¬ 
tures  for  a  year  or  any  long  period  invariably  show  that 
the  warmest  place  is  on  the  hillside  somewhere  above  the 
base.  On  lono;  slopes  on  quiet  nights  there  will  often  be 
temperatures  from  1°  to  14°  higher  than  at  top  or  bottom. 

To  the  fruit  grower  a  thermal  belt  is  a  very  real  thing 
on  a  quiet  night,  when  the  temperature  is  falling  to  the 
danger  point.  If  his  orchard  is  located  on  a  slope  well 
above  the  frosty  bottoms,  yet  at  an  altitude  not  suffi¬ 
ciently  high  to  reach  the  realm  of  high  top  freezes,  his 
fruit  may  pass  safely  through  the  frosty  periods,  while 
elsewhere  the  crop  may  bo  a  total  failure. 

The  following  letter  from  Mr.  J.  B.  Horton,  of  Elkin, 
N.  C.,  is  significant  and  well  worthy  of  publication  here: 

Since  coming  over  here  early  in  July,  I  have  been  making  inquiry 
in  regard  to  fruit  crop  in  this  county  and  find  only  apple  orchards 
planted  above  frost  line  have  full  crop.  Most  of  trees  on  low  land  are 
bearing  light  crops.  I  find  one  orchard  that  has  not  failed  to  bear  full 
crop  since  planted,  perhaps  25  years  ago,  that  has  this  year  300  bushels 
of  Virginia  Beauties  and  other  market  apples.  The  thermal  belt,  or 
frost  line,  is  very  accurately  marked  in  the  apple  crop  this  year,  and 
it  occurs  to  me  that  now  would  be  a  most  excellent  time  for  some 


valuable  demonstration  work  to  be  done  by  you  and  your  assistants 
in  your  branch  of  the  Agricultural  Department.  One  farmer  in  this 
county  has  a  cherry  tree  through  which  the  frost  line  passes  about 
half  way  to  the  top,  and  on  one  occasion  a  full  crop  of  cherries  was 
produced  above  and  none  below  the  line. 


Selected  Bibliography. 

Andre,  C.  Influence  de  l’altitude  sur  la  temperature,  Lyon,  1888. 

Brown,  W.  P.  Winter  temperatures  on  mountain  heights.  (Quar¬ 
terly  Journal  of  the  Royal  Meteorological  Society,  v.  36,  January, 
1910). 

Chickering,  J.  W.,  jr.  Thermal  belts.  (American  Meteorological 
Journal,  v.  1,  1884-85). 

Cox,  H.  J.  Frost  and  temperature  conditions  in  the  cranberry  marshes 
of  Wisconsin.  U.  S.  Weather  Bureau,  Bulletin  T. 

Davis,  W.  M.  Types  of  New  England  weather.  (Annals  of  the  Astro¬ 
nomical  Observatory  of  Harvard  College,  v.  21.  part  2,  1890.) 

Forel,  F.  A.  Variation  de  temperature  avee  Faltitude  (Archives  des 
sciences  physiques  et  naturelles,  v.  18). 

Hann,  J.  Handbook  of  Climatology;  (tr.  by  R.  DeC.  Ward,  1903, 
v.  1). 

Larue,  Pierre.  Sur  le  climat  de  motagne.  (Comptes  rendus  de 
l’Association  Francaise  pour  l’avancement  des  sciences,  1914.) 

Moore,  Sir  John.  Meteorology,  practical  and  applied. 

Morley,  Margaret  W.  The  Carolina  mountains. 

McLeod,  C.  Records  of  difference  of  temperature  between  McGill 
College  Observatory  and  the  top  of  Mount  Royal,  Montreal.  (Pro¬ 
ceedings  of  the  Royal  Observatory.  London,  v.  76.) 

Nevada.  Agricultural  Experiment  Station.  Mount  Rose  weather  ob¬ 
servatory.  1906-1907.  Bulleitn  No.  67,  June.  1908. 

North  Carolina.  State  Weather  Service.  Climatology  of  North  Caro¬ 
lina,  1891  and  1892. 

Rudaux,  Lucien.  Sur  quelques  observations  effectuees  en  montagne 
(Astronomie,  v.  27,  Sept.  1913). 

Seeley,  Dewey  A.  Relation  between  Temperature  and  Crops.  (19th 
Michigan  Academy  of  Science  Report,  1917.) 

U.  S.  Weather  Bureau.  Monthly  Weather  Reviews: 

Thermal  belts,  frostless  zones  or  verdant  zones,  v.  21,  December, 
1893. 

Vertical  Temperature  Gradients,  v.  27,  March,  1899. 

Temperatures  on  Mount  Rose,  Nev.,  v.  33,  October,  1905. 

Temperature  Inversion  in  the  Grand  River  Valley,  Colo.,  v.  43. 
October,  1915. 

Frost  protection,  (a  symposium),  v.  42,  October,  1914. 

Slope  and  valley  air  temperatures,  v.  43,  December.  1916. 

Supplement  No.  9.  Periodical  events  and  natural  law  as  guides  to 
agricultural  research  and  practice.  A.  D.  Hopkins,  1918. 

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Variations  of  temperature  and  pressure  at  summit  and  base  stations 
in  the  Rocky  Mountain  region,  bv  A.  J.  Henry,  vol.  3  and  vol.4. 

Diurnal  system  of  convection,  by  Wm.  R.  Blair,  vol.  6,  part  5. 

Summary  of  free  air  data  at  Mount  Weather,  by  Wm.  R.  Blair,  vol. 
6,  part  4. 

Monthly  Weather  Review,  February,  1918:  Solar  and  sky  radia¬ 
tion  measurements,  by  H.  H.  Kimball. 


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